Method for patterning metal using nanoparticle containing precursors

ABSTRACT

Continuous, conducting metal patterns can be formed from metal nanoparticle containing films by exposure to radiation (FIG.  1 ). The metal patterns can be one, two, or three dimensional and have high resolution resulting in feature sizes in the order of micron down to nanometers Compositions containing the nanoparticles coated with a ligand and further including a dye, a metal salt, and either a matrix or an optional sacrificial donor are also disclosed.

CROSS REFERENCE

This application is a divisional of U.S. Ser. No. 11/736,695, filed Apr.18, 2007, which is a continuation of U.S. application Ser. No.10/450,661 filed on Dec. 15, 2003, which is a National Stage ofPCT/US01/47724 filed on Dec. 17, 2001, all of which claim priority toProvisional U.S. Application Ser. No. 60/256,148 filed on Dec. 15, 2000.The contents of each of these documents are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the patterning of a metal feature usinga metal nanoparticles containing material and exposing it to radiation.

2. Discussion of the Background

Currently available technology for the micro fabrication of metalpatterns includes:

1) use of masks to define patterns of metal by deposition or etching(Shacham-Diamand, Y., Inberg, A., Sverdlov, Y. & Croitoru, N.,Electroless silver and silver with tungsten thin films formicroelectronics and microelectromechanical system applications. Journalof the Electrochemical Society, 147, 3345-3349 (2000));

2) laser ablation of metal films to create patterns;

3) laser direct writing based on pyrollitic deposition of metal fromvapor, solution or solid precursors; (Auerbach, A., On DepositingConductors From Solution With a Laser, Journal of the ElectrochemicalSociety, 132, 130-132 (1985); Auerbach, A., Optical-Recording ByReducing a Metal Salt Complexed to a Polymer Host, Applied PhysicsLetters, 45, 939, 941 (1984); Auerbach, A., Copper Conductors ByReduction of Copper (I) Complex in a Host Polymer, Applied PhysicsLetters, 47, 669-671 (1985); Auerbach, A., Method For ReducingMetal-Salts Complexed in a Polymer Host WIth a Laser, Journal of theElectrochemical Society, 132, 1437-1440 (1985)); and

4) light exposure and development of silver-halide based photographicfilm followed by electroless and electrochemical plating (Madou, M. &Florkey, J., From batch to continuous manufacturing of microbiomedicaldevices. Chemical Reviews, 100, 2679-2691 (2000); M. Madou., Fundamentsof Microfabrication (CRC Press, Boca Raton, 1997); Madou, M., Otagawa,T., Tierney, M. J., Joseph, J. & Oh, S. J., Multilayer Ionic DevicesFabricated By Thin-Film and Thick-Film Technologies. Solid State Ionics,53-6, 47-57 (1992)).

Currently available methods are described, for example, in the followingpublications:

Southward, R. E. et al., Synthesis of surface-metallized polymeric filmsby in situ reduction of(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato) silver(I) in apolyimide matrix. Journal of Materials Research, 14, 2897-2904 (1999);

Southward, R. E. & Thompson, D. W. Inverse CVD, A novel syntheticapproach to metallized polymeric films. Advanced Materials, 11,1043-1047 (1999);

Gu, S., Atanasova, P., Hampden-Smith, M. J. & Kodas, T. T., Chemicalvapor deposition of copper-cobalt binary films. Thin Solid Films, 340,45-52 (1999);

Jain, S., Gu, S., Hampden-Smith, M. & Kodas, T. T., Synthesis ofcomposite films. Chemical Vapor Deposition, 4, 253-257 (1998);

Gu, S., Yao, X. B., Hampden-Smith, M. J. & Kodas, T. T., Reactions ofCu(hfac)(2) and Co-2(CO)(8) during chemical vapor deposition ofcopper-cobalt films. Chemistry of Materials, 10, 2145-2151 (1998);

Calvert, P. & Rieke, P., Biomimetic mineralization in and on polymers.Chemistry of Materials, 8, 1715-1727 (1996);

Hampden-Smith, M. J. & Kodas, T. T., Chemical-Vapor-Deposition ofMetals. 2. Overview of Selective CVD of Metals. Chemical VaporDeposition, 1, 39-48 (1995);

Hampden-Smith, M. J. & Kodas, T. T., Chemical-Vapor-Deposition ofMetals. 1. an Overview of CVD Processes. Chemical Vapor Deposition, 1,8-23 (1995);

Xu, C. Y., Hampden-Smith, M. J. & Kodas, T. T., Aerosol-AssistedChemical-Vapor-Deposition (AACVD) of Binary Alloy (Ag(x)Pd(1)-X,Cu(x)Pd(1)-X, Ag(x)Cu(1)-X) Films and Studies of Their CompositionalVariation. Chemistry of Materials, 7, 1539-1546 (1995); and

Naik, M. B., Gill, W. N., Wentorf, R. H. & Reeves, R. R., CVD of CopperUsing Copper(I) and Copper(II) Beta-Diketonates. Thin Solid Films, 262,60-66 (1995).

The above described methods are limited to direct production oftwo-dimensional patterns, and three-dimensional patterns must be builtup by use of multilayer or multistep processes. Laser direct writing ofmetal lines allows for single step microfabrication of one-dimensionalor two-dimensional patterns, but has mainly involved thermaldecomposition of a metal precursor at a high temperature created byabsorption of laser energy. There is great interest in an ambienttemperature process for forming metal lines by laser writing and fordirectly writing three-dimensional metal patterns.

Swainson et al., in a series of patents, (U.S. Pat. Nos. 4,466,080;4,333,165; 4,238,840; and 4,288,861) described the photoreduction ofsilver by using conventional dyes such as methylene-blue and others assilver photoreducing agents in solution. Silver coatings of surfacesfollowing optical excitation of such silver ion and dye solutions weredescribed. The presence of “certain reducing/chelating agents, such aso-phenanthroline” were described as being a fundamental component of thesystem. Swainson also described that by following similar methods onewould not be able to write continuous metal phases within a solidmatrix. In fact, the introduction to the sections that included themetal photoreduction stated that the previously generally preferredstabilized or solid media are not suitable for the production ofproducts with a material complexity above a certain level. Accordingly,their examples used gaseous and liquid physical states which accordingto Swainson permit increased complexity of products by virtue of theirtransportive capability. In the solid state, the present inventors haveindeed found that Swainson's method does not result in the formation ofcontinuous metal.

Whitesides et al. described a multistep method for the generation ofconductive metal features both in an article: Deng T., Arias, F.,Ismagilov, R. F., Kenis, P. J. A. & Whitesides, G. M., Fabrication ofmetallic microstructures using exposed, developed silver halide-basedphotographic film. Analytical Chemistry, 72, 645-651 (2000); and in U.S.Pat. No. 5,951,881. The key difference between the system described byWhitesides et al. and the system of the present invention is that theyphotochemically generate metal nanoparticles in a gelatin and in asubsequent step they use an electroless deposition of silver on thesilver crystals, so as to develop it (Braun, E., Eichen, Y., Sivan, U. &Ben-Yoseph, G., DNA-templated assembly and electrode attachment of aconducting silver wire. Nature, 391, 775-778 (1998)), thus forming acontinuous metal structure. Moreover, in order to obtain real 3Dpatterns they have to perform multi-step construction of the device. Thesmallest dimension of the lines (30 μm) described by Whitesides et al.is much larger than the one achievable with the method according to thepresent invention.

Reetz et al. described in an article and a patent titled: “Lithographicprocess using soluble or stabilized metal or bimetal clusters forproduction of nanostructures on surfaces” the fabrication via electronbeam irradiation of continuous metal features starting from surfactantstabilized metal nanoparticles (Reetz, M. T., Winter, M., Dumpich, G.,Lohau, J. & Friedrichowski, S. Fabrication of metallic and bimetallicnanostructures by electron beam induced metallization of surfactantstabilized Pd and Pd/Pt clusters. Journal of the American ChemicalSociety 119, 4539-4540 (1997); Dumpich, G., Lohau, J., Wassermann, E.F., Winter, M. & Reetz, M. T. in Trends and New Applications of ThinFilms 413-415 (Transtec Publications Ltd, Zurich-Uetikon, 1998). Bedsonet al., describe the electron beam writing of metal nanostructuresstarting from passivated gold clusters, that were alkylthiol capped goldnanoparticles. Bedson T. R., Nellist P. D., Palmer R. E., Wilcoxon J. P.Direct Electron Beam Writing of Nanostructures Using Passivated GoldClusters. Microelectronic Engineering 53, 187-190 (2000)).

The differences between what is described there and the presentinvention are:

1) Reetz et al's and Bedson et al's processes involve fusion ofnanoparticles rather than the growth of nanoparticles based on thegeneration of metal atoms upon excitation;

2) their starting materials are made solely of stabilized nanoparticles,whereas we teach the use of composite materials in which stabilizednanoparticles are just one of the components;

3) their irradiation method is solely electron-beam irradiation, whilewe teach that using suitable reducing agents our composite materials canbe good precursors for a wide variety of stimulating radiation,electron-beams being just one of them; and

4) their nanoparticles are coated with ligands that provide onlystabilization solubilization properties, while our compositions forelectron beam patterning of metal are composites based on nanoparticles,metal salt, and an excited dye reducing agent, that can be included bycovalent attachment to a ligand on the nanoparticle.

The compositions and methods of excitation of dyes with strongmultiphoton absorption properties have been disclosed by Marder andPerry, U.S. Pat. No. 6,267,913 “Two-Photon or Higher-Order AbsorbingOptical Materials and Methods of Use”.

Some compositions and methods have been disclosed for the multiphotongeneration of reactive species including the photogeneration of silverparticles in a patent application by B. H. Cumpston, M. Lipson, S. R.Marder, J. W. Perry “Two-Photon or higher order absorbing opticalmaterials for generation of reactive species” U.S. patent applicationNo. 60/082,128. The method taught in U.S. patent application No.60/082,128 differs from those of this invention because in the priorapplication there is no mention of the use of metallic nanoparticles asprecursors.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for 1)direct fabrication of one, two or three-dimensional microstructures ofmetal in a single processing step, and 2) the fabrication of nanometerscale metal patterns in one or two dimensional patterns also in a singleprocessing step. Specifically, it is an object of the present inventionto provide a low temperature process for forming metal lines by laserwriting and for directly writing three-dimensional patterns.

These and other objects have been achieved by the present invention thefirst embodiment which includes a method for growth of a pre-nucleatedmetal nanoparticle, comprising:

providing said pre-nucleated metal nanoparticle in a composite;

generating a metal atom by reducing a metal ion by exposure toradiation;

reacting said metal atom with said we-nucleated metal nanoparticle,thereby growing a metal nanoparticle.

Another embodiment of the invention includes a method for growth of apre-nucleated metal nanoparticle, comprising:

forming a film from said pre-nucleated metal nanoparticle, a metal salt,a dye and a polymer matrix;

generating a metal atom by reducing a metal ion of said metal salt byexposure to radiation;

reacting said metal atom with said pre-nucleated metal nanoparticle,thereby growing a metal nanoparticle.

Yet another embodiment of the present invention includes a metalnanoparticle containing composition, comprising:

a ligand coated metal nanoparticle;

a dye;

a metal salt; and

optionally a sacrificial donor.

Another embodiment of the present invention includes a metalnanoparticle containing composition, comprising:

a ligand coated metal nanoparticle;

a dye;

a metal salt; and

a matrix.

A further embodiment of the present invention includes a method,comprising:

subjecting one of the above metal nanoparticles containing compositionsto radiation, thereby effecting a growth of said nanoparticles; and

forming a continuous or semi-continuous metal phase.

The present invention further includes a method, comprising:

forming a film from a metal nanoparticle, a metal salt, a dye and apolymer matrix; and

exposing said film to radiation, thereby producing a pattern of aconductive metal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1. Schematic illustration of case 1 growth process.

FIG. 2. Energy level scheme for sensitized metal ion reduction.

FIG. 3. Illustration of writings of metal features in a nanoparticlecomposite.

FIG. 4. Optical transmission image, (top view) of a 3D structure(200×200×65 μm) written in a polymer matrix.

FIG. 5. Optical image of the same structure shown in FIG. 4 on a largerscale.

FIG. 6. SEM image of a 3D metallic silver microstructure formed bytwo-photon writing in a composite film.

FIG. 7. XPS spectrum and image of a set of silver lines.

FIG. 8. Schematic drawing of the attachment of a ligand capped metalnanoparticle to a thiol functionalized glass substrate.

FIG. 9. TEM images illustrating growth of metal nanoparticle in acomposite film upon exposure to either one or three laser pulses from ans pulsed laser.

FIG. 10. Silver ribbon written with a two-photon irradiation.

FIG. 11. Silver lines written using a one-photon excitation.

FIG. 12. Optical micrograph of a copper square written by two-photonexcitation.

FIG. 13. Spectrum of sample from control experiment.

FIG. 14. SEM picture of the corner of a 3D metallic silver structurewritten using two-photon excitation.

FIG. 15. TEM image of chemically synthesized nanoparticles used as aprecursor in the composites.

FIG. 16. Examples of a square and a line written and imaged using anSEM.

FIG. 17. Laser and electron-beam induced growth of silver nanoparticlesin a nanoparticle/salt composite.

FIG. 18. Transmission optical microscopy of a line written in a PVK filmdoped with AgBF₄ and nAg12.

FIG. 19. Reflection image of a silver square embedded in a polymernanocomposite.

FIG. 20. Schematic drawing of the slide/polymer/microfabricated lineconfiguration used to measure the conductivity of the grown wires.

FIG. 21. Plot of an I(V) curve.

FIG. 22. Metallic structures fabricated in nanocomposites by two-photonscanning laser exposure.

FIG. 23. Optical set ups for the writing and reading of holograms.

FIG. 24. Reconstructed holographic image.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the use of metal nanoparticlecontaining films in conjunction with exposure to radiation to activatethe growth and fusion of such particles to form continuous conductingmetal patterns. In the process, one, two, or three dimensional,continuous conducting metal wires or other patterns may be formed.

The novel metal nanoparticle systems and methods of exposure for thedirect patterning of metal in three dimensions and with high resolutionin the order of microns to nanometers, are unprecedented. Subjectingcertain nanoparticle containing compositions to forms of excitation canresult in growth of these particles, leading ultimately to a continuous(or semi-continuous) metal phase. Patterned excitation leads toformation of corresponding metallic patterns. Methods based on two typesof compositions and involving free space optical exposure, near-fieldoptical exposure or exposure with ionizing radiation, such as electronsfrom the conductive tip of an scanning probe microscope are describedherein.

In the process of the present invention, radiation from differentsources results in different resolution. For example, a feature sizes ofdown to 300 nm can be achieved using a blue laser and one photonexcitation. A feature size of down to 100 nm, and preferably down to 50nm may be achieved using a near field light source. If two photonexcitation is used, the feature size may be down to 100 nm, preferably50 nm. Electron-beams allow for a resolution of 10 nm to 300 nm. Focusedion beam allow for a feature size of down to 5 to 10 nm. An extremelysmall feature size of down to 5 nm may be achieved using a ScanningProbe Microscope tip.

The nanoparticles used in the method according to the present inventionare mainly those coated with organic ligands. By ligand, we mean anymolecule or ion that has at least one atom having a lone pair ofelectrons that can bond to a metal atom or ion. By ligand, we also meanunsaturated molecules or ions that can bond to a metal atom or ion.Unsaturated molecules or ions possess at least one π-bond, which is abond formed by the side-by-side overlap of p-atomic orbitals on adjacentatoms. One example of an organic ligand for silver, gold, or coppernanoparticles is an n-alkylthiol ligand, which preferably has an alkylchain length of 4 to 30 carbons. The coatings of the nanoparticlesrender them soluble in common organic solvents and processable bysolution processing techniques. These coatings can also stabilize thenanoparticle with respect to aggregation and/or coalescence of the metalcore of the particle. Throughout this disclosure, the term ligand coatednanoparticle is used to describe such stabilized particles. Furthermore,according to the present invention, nanoparticles with two or moredifferent types of ligands, such as two alkylthiol ligands of differentlengths exhibit increased solubility in organic solvents and polymermatrices, such as poly(vinyl carbazole) and a reduced tendency towardsthe formation of aggregates resulting from inter-digitation of ligands,compared to nanoparticles coated with one type of alkylthiol ligand,which are known to form aggregates with interdigitated ligands. Voicu,R., Badia, A., Morin, F., Lennox, R. B. & Ellis, T. H., Thermal behaviorof a self-assembled silver n-dodecanethiolate layered material monitoredby DSC, PTIR, and C-13 NMR spectroscopy. Chemistry of Materials, 12,2646-2652 (2000); Sandhyarani, N., Pradeep, T., Chakrabarti, J., Yousuf,M. & Sahu, H. K. Distinct liquid phase in metal-cluster superlatticesolids. Physical Review B, 62, 8739-8742 (2000); Sandhyarani, N. &Pradeep, T., Crystalline solids of alloy clusters. Chemistry ofMaterials, 12, 1755-1761 (2000); Badia, A. et al., Self-assembledmonolayers on gold nanoparticles. Chemistry—a European Journal, 2,359-363 (1996)). The use of nanoparticles with two or more types ofligands for the formation of a metal nanoparticle/polymer composite isadvantageous because a higher concentration of particles may be achievedand the optical quality of the composite may be higher, since thereduction of aggregation leads to lower optical scattering compared tocomposites including nanoparticles with a single type of alkylthiolligand. The ligand coated nanoparticles can be easily spin coated,casted or inserted as dopants into organic films or diffused intoinorganic glasses prepared via sol-gel chemistry. Two classes ofcompositions are described here. They differ in the nature of thematrix:

Class I is a composition in which the ligand coated nanoparticlesthemselves are the matrix.

Class II is a composition in which a polymer, a glass or a highlyviscous liquid is the matrix, and the nanoparticles are dopants.

It is known that photochemical reduction of metal ions, such as silverions (Ag⁺), by suitable dye molecules leads to the formation of Ag⁰atoms and the nucleation of small, nanometer-sized particles of Ag⁰.However, a key problem with past attempts to photochemically writecontinuous, conducting metal patterns is that the limited supply ofmetal ions in the precursor material, as well as the high degree ofexcitation required to provide nucleation centers makes the growth ofcontinuous metal quite difficult. Particles formed are typically notinterconnected and do not form a conductive path. With this type ofproduct one would have to perform an additional wet chemical processingstep to “develop” the particles to form conductive lines. However,according to the present invention, incorporation of ligand-coatedsilver nanoparticles into the precursor material overcomes this problemby providing both initial nucleation sites for growth of the metal, andsome starting volume fraction of metal. Upon sufficient growth, thesurface coverage of the ligand on the nanoparticle becomes insufficientto prevent the particle from undergoing fusion with other neighboringgrowing particles to form a larger metal phase. The surface coverage ofthe ligand on the nanoparticle becomes insufficient to prevent theparticle from undergoing fusion with other neighboring growing particlesto form a larger metal phase. Thus, upon sufficient growth thenanoparticles become highly interconnected and form well conductingpathways. The approach disclosed here allows for direct and simple,photochemical fabrication of microstructures of conductive metal, at lowtemperatures, such as ambient room temperature (21° C.).

One type of composition that is effective in the method according to thepresent invention involves a composite containing a) metalnanoparticles, b) a metal salt and c) a dye, capable of excited statereduction of the metal ions and possessing appropriate light absorptionproperties, and d) a polymer host material. Many variations on thecomposition of this composite are possible, including: 1) the type ofmetal nanoparticle, 2) the type of metal ion, 3) the counterion of themetal salt, 4) the structure of the dye, 5) whether or not a polymerhost is used, and 6) the type of polymer host if one is used. By theterm dye, we mean a molecule or ion that absorbs photons withwavelengths ranging from 300 nm to 1.5 μm. Depending on the composition,metal nanoparticle/polymer nano-composites with good light transmissionproperties and large thickness, up to hundreds of micrometers,preferably up to 500 micrometers, more preferably up to 700 micrometersand most preferably up to 900 micrometers, can be prepared. In themethod according to the present invention, such composite can be exposedin a patterned manner with optical radiation or with ionizing radiationbeams, either by use of a mask or by suitable scanning of a highlyconfined beam of radiation, to produce a pattern of conductive metal.

According to the present invention, compositions incorporating dyemolecules possessing two-photon absorption cross sections greater thanor equal to 1×10⁻⁵⁰ cm⁴ photon⁻¹sec⁻ and capable of excited-statereduction of the metal ions can be used to create three dimensionalpatterns of conductive metal. Examples of dye molecules with largetwo-photon absorption cross sections are described in U.S. Pat. No.6,267,913 which is included herein by reference. In the presentembodiment, a tightly focused, high intensity laser beam tuned to thetwo-photon absorption band of the dye is used to localize thephotoactivated growth of metal to a small volume. The ability to achievehigh 3D spatial resolution arises from the fact that the probability ofsimultaneous absorption of two photons depends quadratically on theintensity of the incident laser light. If a tightly focused beam isused, the intensity is highest at the focus and decreases quadraticallywith the distance (z) from the focal plane, for distances larger thanthe Rayleigh length. Thus, the rate at which molecules are exciteddecreases very rapidly (as z⁻⁴) with the distance from the focus and theexcitation is confined in a small volume around the focus (of the orderof λ³, where λ is the wavelength of the incident beam). The sample orthe focused beam can be scanned and the intensity controlled to map outa three dimensional pattern of exposure and to produce 3D structurescomprised of continuous metal.

In a preferred embodiment, Ag nanoparticles (with a ligand coating) arecombined with AgBF₄ salt, and an electron deficient two-photon absorbingdye in polyvinylcarbazole, to form a composite. In an example ofexposure with radiation for writing of a metal pattern, 100 fs laserpulses at a wavelength of 730 nm are focused onto the film resulting inthe formation of reflective and conductive Ag metal at the points ofexposure. Preferably, the laser wavelength ranges from 157 nm to 1.5 μmfor one-photon excitation and from 300 nm to 3.0 μm for two-photonexcitation. The pulse width of the laser is preferably in the order of≦1 μs to 10 fs for two-photon excitation. Arbitrary patterns of Ag metalcan be written by moving the point of focus in the film. Writing ofmicroscale lines, rectangular shapes and various 3D patterns of metallines has been accomplished with this method. Many variations in thestep of exposure with radiation are possible, as would be known to thoseskilled in the art of radiation induced change of materials properties.For example, electron beams, electrical current via a scanning probetip, focused ion beams, γ-radiation, x-rays, UV-rays, VUV-rays, neutronbeams, and neutral atom beams may be used in the method of the presentinvention.

Formation and Growth of Metal Nanoparticles

It is known that the formation of alkylthiolate coated metalnanoparticles proceeds via a nucleation-growth mechanism (Hostetler, M.J. et al., Alkanethiolate gold cluster molecules with core diametersfrom 1.5 to 5.2 nm: Core and monolayer properties as a function of coresize. Langmuir, 14, 17-30 (1998)) that involves the formation of alayered stoichiometric compound as a first step as illustrated below forAg:nAg⁺+nRSH→(AgSR)_(n)+H⁺followed by a second step involving growth. The second step can be dueto the presence of silver zero atoms:(AgSR)_(n)+mAg⁰→Ag_(n),(SR)_(n)with n′=n+mor to the presence of an agent that reduces the metal ions of thelayered compound themselves:(AgSR)_(n)→Ag_(n)(SR)_(m)+m′RSSRwith 2 m′=n−m

Once generated, these nanoparticles are soluble materials that areprocessable with standard methods. In particular, their solubility inorganic solvents allows for a multiplicity of processing techniquesbased on which films of nanoparticles or solid matrices withincorporated nanoparticles can be created. We teach that, with such ananoparticle film or composite, the growth of nanoparticles may bedriven such that they increase in size, and contact and fuse with othernanoparticles. When this process occurs to a sufficient extent, then acontinuous metallic feature (single or polycrystalline) will be formed.

One important contribution of the present invention is that it teachesthe materials and exposure conditions that allow the growth ofpre-nucleated metal nanoparticles in solid state. By the termpre-nucleated metal nanoparticle we mean a metal nanoparticle which hasbeen nucleated and grown in a preceding synthetic process. Theseconditions allow nanoparticles to grow to the point wherein theycollapse in a continuous metallic feature.

Several growth processes are disclosed that vary in the method by whichthe metal atom (zero oxidation number) is generated from its ion.

The first case (case 1) makes use of the generation of the metal atomfrom the metal ion using an electron beam. The electron beam candirectly reduce the silver ion or can generate a radical anion that thenreduces the metal ion or can ionize a molecule and the electron thenreduces the metal ion.

An advantage of case 1 is the versatility in the metal line resolutionthat can be achieved, which can range from several microns (with the useof a mask and a large electron beam) to few nanometers (with the use ofconductive scanning probe microscopy tips, for example). FIG. 1 is aschematic illustration of a case 1 growth process. In the upper drawingan injected electron reduces a metal ion; in the lower part it generatesa radical anion that subsequently reduces the metal ion. In particular,conductive tip Atomic Force Microscopy, in which the tip of themicroscope approaches a film in tapping mode, can be used as source ofelectrons. Once it is positioned within few nanometers away from thesurface of the nanoparticles it injects electrons into the nanoparticlefilm to generate metal lines whose thickness may be just a fewnanometers.

The second case (case 2) is that wherein metal ions are reduced to theirzero oxidation number through a local increase in temperature which iscaused by absorption of light energy (preferably a laser beam) by a dyemolecule and the transfer of the absorbed energy to heat. Materials andMethods for the non-linear local heating of materials are described inU.S. Pat. No. 6,322,931 which is incorporated herein by reference.

The third case (case 3) is to photoexcite a molecule so as to create anexcited state, thus increasing the reducing potential of the molecule bya sufficient amount that it can reduce the metal ion, whereas the groundstate could not. In this process the dye is oxidized so, in many cases,a sacrificial donor may be required in order to regenerate it. FIG. 2illustrates an energy level scheme for sensitized metal ion reduction.In the first step (black) an electron is promoted from the highestoccupied molecular orbital (HOMO) level of the dye to one of its excitedstates. From this level the electron either goes directly to the metalion (red) or first to the lowest unoccupied molecular orbital (LUMO) ofan electron transporting material (blue) and then to the metal ion.Subsequently, an electron may transfer (green) from the HOMO of thesacrificial donor to the HOMO of the dye, thereby regenerating theneutral dye. The sacrificial donor and the electron transportingmaterial are not necessary.

The feature size resolution achievable in this case depends on the typeof photo excitation. The lower limit on the feature size can be severalmicrons is diffraction limited for one photon (case 3a) irradiation, ispotentially smaller for multi-photon irradiation, due to thresholdingeffects (case 3b), and is in the order of tens of nanometers for nearfield irradiation (case 3c). In this case the limit is determined by thenear-field source dimension and its position relative to the film.

FIG. 3 illustrates the writing of metal features in a nanoparticlecomposite. The red cone represents the laser beam and the darker spot atits end represents the focus of the beam. The gray rectangle is thecomposite film containing the dye and the salt in it, while the bluecircles represent the nanoparticles. Upon exposure, growth andcoalescence, a metal pattern is formed. In the upper part (a), the metalatoms are formed in the beam focus and they start to migrate towardnanoparticles, then (b) the nanoparticle starts to grow, and finally (c)a continuous metal feature is formed. This scheme is appropriate to case2 and 3 methods.

Preferred Embodiments

Preferred examples will be given in the following section to illustratemethods of fabrication of metal. These examples are by no meansexhaustive and it should be clear to one skilled in the art thatnumerous other procedures can be employed based upon the basicprinciples of the invention disclosed herein. Two different classes ofcompositions can be used to generate metal features. In the first classthe metal nanoparticles act as their own matrix and in the second classthe metal nanoparticles are dopants in a host matrix.

Class I

In the first embodiment the material is composed of:

i) ligand coated metal nanoparticles coated by one or more types oforganic ligands. In some cases it is advantageous to use a mixture oforganic ligands, as described above. In addition, molecules as describedin (ii) (below) could be attached to one or more types of ligandscoating the particle.

ii) a molecule (dye) whose molecular orbital energy levels are suitablefor photoreduction of the corresponding metal salt or whose linear ornonlinear optical absorption is able to generate the sufficient heat tocause reduction the metal salt. This component can be dissolved in thenanoparticle matrix or covalently bonded to the nanoparticle as one ofthe ligands, or as the only ligand;

iii) a metal salt; and

iv) a sacrificial donor, that is a molecule whose molecular orbitallevels are of appropriate energy to reduce the cation of the dyedescribed in (ii) above, which is formed upon photoreduction of themetal ion or upon electron-beam exposure. In this manner, the originaldye can be regenerated and can once again act as a reducing agent ofmetal. The component may be part of the host matrix structure. In somecases this component may not be necessary.

Preferred concentrations (in weight percent, based on the total weightof the composition) for each component of the class I system are asfollows and are chosen so as to add to a total of 100%:

Component (i): 55 to 100%, including all values and subvaluestherebetween, especially including 60, 65, 70, 75, 80, 85, 90 and 95%;

Component (ii): 0 to 15%, including all values and subvaluestherebetween, especially including 2, 4, 6, 8, 10, 12 and 14% (0 appliesfor the case where the nanoparticles have dye terminated ligands intheir outside shell);

Component (iii): 0 to 15%, including all values and subvaluestherebetween, especially including 2, 4, 6, 8, 10, 12 and 14%;

Component (iv): 0 to 10%, including all values and subvaluestherebetween, especially including 2, 4, 6, and 8%.

Class II

In the second embodiment a material acts as a host matrix in which theother components i)-iv) are dispersed or dissolved:

v) a matrix that dissolves all the other components. This matrix can be:

-   -   a) a polymer;    -   b) a glass;    -   c) a highly viscous liquid;    -   d) a liquid crystalline material or polymer, or mesoscopic        phase; and    -   e) a porous crystalline or amorphous solid.

In the case (a) of component (v) there could be circumstances in whichit is particularly advantageous to add an additional component (vi):

vi) a plasticizer, that is a molecule capable of lowering the glasstransition temperature of the polymer, thereby rendering its mechanicalproperties more suitable for the application.

In both cases the component (ii) is not necessary when the source ofirradiation is an electron beam.

Preferred concentrations (in weight percent, based on the total weightcomposition) of the for each component of the class II system are asfollows and are chosen so as to add to a total of 100%:

Component (i): 0.05% to 25%, including all values and subvaluestherebetween, especially including 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 10, 15and 20%;

Component (ii): 0 to 15%, including all values and subvaluestherebetween, especially including 2, 4, 6, 8, 10, 12 and 14% (0 applieswhere the nanoparticles have dye terminated ligands in their outsideshell, or either the host or the plasticizer have a suitable dye assubunit);

Component (iii): 0 to 25%, including all values and subvaluestherebetween, especially including 5, 10, 15 and 20%;

Component (iv): 0 to 60%, preferably from 20% to 60%, including allvalues and subvalues therebetween, especially including 10, 20, 30, 40and 50%;

Component (v): 0.5-99.5%, including all values and subvaluestherebetween, especially including 10, 20, 30, 40, 50, 60, 70 and 80%;and

Component (vi): 0 to 70%, including all values and subvaluestherebetween, especially including 10, 20, 30, 40, 50 and 60%.

Description of the Components

Component (i): Metal Nanoparticles

Preferred examples of component (i) are:

i1) metal (e.g. silver, gold, copper, and iridium) nanoparticles withdimensions from 1 to 200 nm (diameter) coated with organic ligands(Kang, S. Y. & Kim, K., Comparative study of dodecanethiol-derivatizedsilver nanoparticles prepared in one-phase and two-phase systems.Langmuir, 14, 226-230 (1998); Brust, M., Fink, J., Bethell, D.,Schiffrin, D. J. & Kiely, C., Synthesis and Reactions of FunctionalizedGold Nanoparticles. Journal of the Chemical Society—ChemicalCommunications, 1655-1656 (1995); Brust, M., Walker, M., Bethell, D.,Schiffrin, D. J. & Whyman, R., Synthesis of Thiol-Derivatized GoldNanoparticles in a 2-Phase Liquid-Liquid System. Journal of the ChemicalSociety—Chemical Communications, 801-802 (1994));

i2) nanoparticles composed of alloys of metals coated with organicligands (Link, S., Burda, C., Wang, Z. L. & El-Sayed, M. A., Electrondynamics in gold and gold-silver alloy nanoparticles: The influence of anonequilibrium electron distribution and the size dependence of theelectron-phonon relaxation. Journal of Chemical Physics, 111, 1255-1264(1999); Link, S., Wang, Z. L. & El-Sayed, M. A., Alloy formation ofgold-silver nanoparticles and the dependence of the plasmon absorptionon their composition. Journal of Physical Chemistry B, 103, 3529-3533(1999));

i3) uncoated metal nanoparticles (for the second embodiment) (Hellmann,A. & Kreibig, U., Optical properties of embedded metal nanoparticles atlow temperatures. European Physical Journal—Applied Physics, 10, 193-202(2000)); and

i4) metallic nanoshells whose cores are semiconductor, metal oxide,silicate, polymer, or biopolymer nanoparticles and whose outer shellsare metallic, the metallic part being with or without (for the secondembodiment) an organic coating (Wiggins, J., Carpenter, E. E. &O′Connor, C. J., Phenomenological magnetic modeling of Au:Fe:Aunano-onions. Journal of Applied Physics, 87, 5651-5653 (2000);Carpenter, E. E. et al., Synthesis and magnetic properties ofgold-iron-gold nanocomposites. Materials Science and Engineeringa—Structural Materials Properties Microstructure and Processing, 286,81-86 (2000)).

Components i1, i2, i3 are made of nanoparticles that can be coated byorganic ligands. These ligands are molecules that are essentiallycomposed of three parts in the following scheme: A-B—C.

Part A is a molecular or ionic fragment that has at least one atomhaving a lone pair of electrons that can bond to a metal nanoparticlesurface, or is an unsaturated molecular or ionic fragment that can bondto the metal nanoparticle surface, and includes a point of attachment toconnect the fragment to B. Some examples include: ^(⊖)S—, ^(⊖)O—,^(⊖)O₂C—, ^(⊖)S—S—R, ^(⊖)O₃S—, ^(⊖)S₂C—NR—, ^(⊖)O₂C—NR—, P(R₁R₂)—,N(R₁R₂)—, O(R₁)—, P(OR₁)(OR₂)O—, and S₂(R)—, where R, R₁, and R₂ may beindependently selected from the group consisting of —H, a linear orbranched alkyl chain containing 1 to 50 carbon atoms, phenyl or otheraryl groups, and hetero aromatic groups.

Part B is an organic fragment that has two points of attachment, one forconnecting to part A and one for connecting to part C. This fragmentserves to provide bulk around the nanoparticle to help stabilize itagainst fusing with other nanoparticles. Part B can be nothing (a singlebond) or can be independently selected from the group consisting of amethylene chain with 1 to 50 carbon atoms, a phenylene chain with 1 to20 phenyls, a thiophenylene chain with 1 to 20 thiophenylenes, phenylenevinylene chains with 1 to 20 phenyl vinylenes, branched hydrocarbonchains with 2 points of attachment, ethylene oxide chains with 1 to 20ethylene oxides, oligo(vinyl carbazole) chains with 1 to 20 vinylcarbazole units and points of attachment at each end of the chain.

Part C is a molecular fragment with one point of attachment thatconnects to fragment B. This group may be used to impart specificfunctions to the exterior of the ligand coated nanoparticle such as,compatability with a matrix, photoreducing properties, two-photonabsorption properties, self-assembly properties, chemical attachmentproperties. Part C can be independently selected from the groupconsisting of —H, phenyl, naphthyl, anthryl, other aryl groups,N-carbazoyl, α-fluorenyl, —SiOR₃, —SiCl₃, any group described as apossible Part A fragment, photoreducing dyes, two-photon absorbingchromophores, a multi-photon absorbing chromophore methylene blue,oligonucleotide strand, peptide chain, or any group described as apossible part B fragment where one of the points of attachment issubstituted with a hydrogen.

The preferred nanoparticles of the present invention may have a mixtureof two or more types of ligands, each one with its own characteristicgroups and functionality.

For the sake of clarity some specific examples of ligands that have beenused for class (i1) are mentioned hereafter:

Ligand Ligand structure Ligand chemica1 name label

Octanethiol I₁

Dodecanethiol I₂

Heptanethiol I₃

8-(9H-carbazol-9-yl)octane-l- thiol I₄

8-(9H-carbazo1-9-y1)dodecane-1- thiol I₅

3-mercaptopropanoic acid I₆

Bis[2-(dimethylamino)ethyl]2- mercaptopentadioate I₇

3-{2,5-bis[(E)-2-(4- formyl-(phenyl)ethenyl]phenoxy}propyl-4-(1,2-dithiolan-3- yl)butanoate I₈

Examples of preferred metal and ligand combinations are the following:

Metal Ligand Given name silver I₁ nAg1 silver I₂ nAg2 silver I₃ nAg3silver I₄ nAg4 silver I₇ nAg5 silver I₁ + I₄ nAg6 silver I₁ + I₂ nAg7silver I₁ + I₇ + I₄ nAg8 silver I₁ + I₄ + I₈ nAg9 gold I₁ nAu1 gold I₂nAu2 copper I₁ nCu1 copper I₁ nCu2

Component (ii) Photoreducing Dyes

Preferred examples of component (ii) are:

Class 1: Centrosymmetric Bis(aldehyde)-bis(styryl)benzenes

R₁ = H R₂ = H 1a R₁ = OCH₃ R₂ = H lb R₁ = OCH₃ R₂ = OCH₃ 1c R₁ = OC₁₂H₂₅R₂ = H 1d R₁ = OC₁₂H₂₅ R₂ = OCH₃ 1eClass 2: Non-Centrosymmetric Bis(aldehyde)-bis(styryl)benzenes

R₁ = H R₂ = H R₃ = H 2a R₁ = OCH₃ R₂ = H R₃ = H 2b R₁ = OCH₃ R₂ = OCH₃R₃ = H 2c R₁ = OC₁₂H₂₅ R₂ = H R₃ = H 2d R₁ = OC₁₂H₂₅ R₂ = OCH₃ R₃ = H 2eClass 3: Centrosymmetric Acceptor Terminated bis(styryl)benzenes

R₁ = H R₃ = H

1a R₁ = OCH₃ R₃ = H

1b R₁ = OCH₃ R₃ = OCH₃

1c R₁ = OC₁₂H₂₅ R₃ = H

1dClass 4: Non-Centrosymmetric Acceptor Terminated Bis(styryl)benzenes

R₁ = H R₂ = OCH₃ R₃ = H

1a R₁ = OCH₃ R₂ = OC₁₂H₂₅ R₃ = H

lb R₁ = OCH₃ R₂ = H R₃ = OCH₃

1c R₁ = OC₁₂H₂₅ R₂ = OCH₃ R₃ = OCH₃

leClass 5: Other Dyes

The dye can be a donor-acceptor dye such as those described in U.S. Pat.Nos. 5,804,101; 6,090,332; 5,670,090; 5,670,091 and 5,500,156 which areincluded herein by reference.

Component (iii:) Metal Salts

Preferred examples of component (iii) are any metal(I) soluble salt,including silver tetrafluoroborate (AgBF₄); silver hexafluoroantimonate(AgSbF₆); silver diethyldithiocarbamate (C₃H₁₀NS₂Ag); silver nitrate(AgNO₃); trimethyl phosphite cuprous iodide (ICuP(OCH₃)₃); andchlorotrimethyl phosphite gold (C1AuP(OCH₃)₃).

Component iv): Matrices

The main requirement of this component is to have the ability todissolve all the other components and to form a homogeneous composite.

Preferred examples of component (v) are:

a) Polymer a₁: poly(9-vinylcarbazole)

In most of the examples given below the polymer actually used was thesecondary standard (Aldrich chemicals) whose M_(n)=69,000;

Polymer a₂:poly(2-{[11-(9H-carbazol-9-yl)undecanoyl]oxy}ethyl-2-methylacrylate)PCUEMA

Polymer a₃: poly (4-chloro styrene); and

Polymer a₄: poly (methylmethacrylate) PMMA;

b) SiO_(x), Organically Modified SiO_(x) Materials, TiO_(x),(SiO_(x))_(n)(TiO_(x))_(m)

c) Viscous Liquid Host:

R = CH₃ c₁ R = OCH₃ c₂*

Other Components

Preferred examples of component (iv) and of component (vi) areethylcarbazole which is a good plasticizers for polyvinyl carbazole, anda sacrificial donor;

terminal di(9-carbazoyl) alkanes which are good plasticizer andsacrificial donors;

0≦n≦10and the following molecule which is a sacrificial donor:

Applications of the present invention include: writing of metal linediffraction gratings for light waves in integrated optics, patterning ofmicroelectrode arrays for applications in electrochemistry or biology,patterning of metal wires for integrated circuit interconnection, forexample in hard wiring of security codes on chips, and in chip repair.Additional applications include: fabrication of nanometer size metalwires, single electron transistors, and other components fornanoelectronics applications; 3D interconnection of electroniccomponents in multilevel integrated circuits; fabrication of metallicdevices for microsurgical applications; antennae and arrays thereof forterahertz radiation, formation of mirrors of different angles ofinclination within a thin film metallic photonic crystal and photoniccrystal waveguides, and metallic microsensors, micro-resonators andmicro-electromechanical structures. This invention can be used for thewiring of nanoscale and single molecule based electronic devices.

Further, the present invention offers the following advantages over thecurrently available technology:

i) Continuous metal lines can be formed in three dimensional patternswith a resolution in the micro- or nanoscale with few limitations on theshape of the pattern.

ii) The process does not require the generation of high temperatures asneeded in pyrollytic processes, and thus can be utilized in theintegration of nanoscale devices or in conjunction with thermallysensitive substrates.

iii) Metal patterns or structures can be produced on a wide variety ofsubstrates. Preferred substrates are silicon, glass or plasticsubstrates, all of which may be covered with, for example,indium-tin-oxide (ITO). Further preferred substrates are Au, Ag, Cu, Al,SiO_(x), ITO, a hydrogel or a biocompatible polymer.

iv) The material systems are easy to process and simple to handle, asopposed to highly toxic gas phase organometallic precursors as typicallyused in chemical vapor deposition.

v) Inert atmospheres are not required.

vi) High vacuum equipment is not needed.

vii) The fact that the process is thresholded allows the sample to behandled under ambient lighting and thermal conditions, thus giving thesamples exceptional long-term stability, for example, a shelf life of 8months in the dark.

However, the process of the present invention is not limited to ambienttemperatures. If Class I compositions are used, a temperature range offrom −270 to 200° C. is preferred. If Class II compositions are used, atemperature range of from −250 to 150° C. is preferred.

Thus, the present invention relates to a novel process for directlywriting three-dimensional metal patterns in a material requiring lowenergy as described in Examples 20 and 21, below and low temperature asstated above. The versatility of the compositions with regard to thetype of metal nanoparticles used and the type of dye offers manypossibilities for engineering of materials for specific applications.

There are many possible applications that can be embodied based on thepresent invention.

One set of applications involves the ability to induce large changes inthe physical properties in a matrix generated by the presence ofdispersed nanoparticles (1-100 nm), dispersed small metal island (100nm-100 μm), quasi-continuous (percolated) metal or continuous metallines. These modifications alter the optical properties, such asrefractive index of a solid state matrix, and such changes in propertiesare useful in optical data storage, in creating diffractive opticaldevices, or in defining waveguiding regions for integrated optics, orwriting of metal line diffraction gratings for light waves in integratedoptics.

This invention can be used for optical data storage in many formats.Information can be stored in 3D using two-photon excitation to writebits comprised of regions containing metal nanoparticles or metalislands. A focused beam is useful in this regard, but crossing beams orinterfering beams, such as in holography, can be employed.

Another example of optical data storage is where the photosensitivemetal nanoparticle composite is used as an optical recording layer forrecordable compact disk-like applications.

A very attractive application is for ultra-high density 2D optical datastorage using near field light source to write very small bits (˜100 nmor smaller).

Other optical applications include: fabrication of reflectivepolarizers, switchable gratings, and micromirrors.

A second set of applications of the present invention uses directpatterning of conductive metal features. They include: patterning ofmicroelectrode arrays for applications in electrochemistry or biology,patterning of metal wires for integrated circuit interconnection, forexample in hard wiring of security codes on chips, and in chip repair.Additional applications include: fabrication of nanometer size metalwires, single electron transistors, and other components fornanoelectronics applications; 3D interconnection of electroniccomponents in multilevel integrated circuits; writing of contacts onsoft materials such as organic light emitting diodes or organic fieldeffect transistors; fabrication of metallic devices for microsurgicalapplications, such as needles and stents (McAllister, D. V., Allen, M.G. & Prausnitz, M. R., Micrafabricated microneedles for gene and drugdelivery. Annual Review of Biomedical Engineering, 2, 289-313 (2000);Polla, D. L. et al., Microdevices in medicine. Annual Review ofBiomedical Engineering, 2, 551-576 (2000); Santini, J. T., Richards, A.C., Scheidt, R., Cima, M. J. & Langer, R., Microchips as controlleddrug-delivery devices. Angewandte Chemie-International Edition, 39,2397-2407 (2000); Rymuza, Z., Control tribological and mechanicalproperties of MEMS surfaces. Part 1: critical review. MicrosystemTechnologies, 5, 173-180 (1999)); and micro-electromechanical structures(Walker, J. A., The future of MEMS in telecommunications networks.Journal of Micromechanics and Microengineering, 10, R1-R7 (2000);Spearing, S. M., Materials issues in microelectromechanical systems(MEMS). Acta Materialia, 48, 179-196 (2000); Lofdahl, L. & Gad-el-Hak,M., MEMS applications in turbulence and flow control. Progress inAerospace Sciences, 35, 101-203 (1999)). The materials and methods ofthis invention can be used for the wiring of nanoscale and singlemolecule based electronic devices (Quake, S. & Scherer, A., From micro-to nanofabrication with soft materials. Science, 290, 1536-1540 (2000)).

Yet other applications can include uses of written metal features inhybrid electrooptical applications, where both the electrical andoptical properties are exploited. An example could be an electrode arrayshaped so to act as a diffractive grating that may be backfilled byliquid crystalline material whose alignment is controlled by the appliedfield. The liquid crystal alignment would control the optical propertiesof the grating.

Writing of conductive metal features is also of advantage toapplications in microfluidics. For example, in the fabrication ofelectroded channels to control fluid flow, to drive electrophoreticseparations, to drive electrochemical reactions, or to monitor thedielectric properties of the channel contents.

Another application of the invention is the patterning or fabricating oftemplates (Ostuni, E., Yan, L. & Whitesides, G. M., The interaction ofproteins and cells with self-assembled monolayers of alkanethiolates ongold and silver. Colloids and Surfaces B—Biointerfaces, 15, 3-30 (1999))which can be used for deposition, self-assembly, or templated growth ofother materials or compounds. For example, patterned metals surfaces canbe used for the generation of patterned arrays of self-assembledmolecules such as thiols, carboxylic acid or other functionalizedcompounds. One can drive reactions at the metal surfaces by using gasphase, solution phase or solid phase reactants. The patterned surfacescan also be exploited for the patterned catalysis of chemical reactions.

Yet another application of the ability to write metal features in a freeform fashion is to create electrode patterns which can be used to directthe growth and interconnection of neurons or other types of cells.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only, and are not intended to belimiting unless otherwise specified.

EXAMPLES

Discussion of the Examples

The following discussion is meant to encompass a set of examples of someimportant experiments and to assist in the understanding of the examplessection.

This discussion mainly focuses on the possibility to write 3D metallicpatterns with multiphoton irradiation (class II, case 3). This, is agood test for all other classes and cases described above. In fact, mostof the steps involved in the present invention are common to all thedifferent cases described and namely they are

1. the synthesis of highly soluble nanoparticles,

2. the preparation of a homogeneous and optical quality matrix, and

3. the post-writing processing and characterization.

These steps are common to all different kinds of writing processes. Thesolution of the problems involved in these parts constitutes a largepart of the present invention.

To generate a homogeneous matrix with good optical quality it isnecessaries to find (i) a solvent or a solvent mixture capable ofdissolving all the components and (ii) a matrix (a polymer) that iscapable of dissolving all the components in solid state. Preferredsolvents are chloroform, dichloromethane, acetonitrile, acetone, water,hexane, heptane, pentane, toluene, dichlorobenzene, dichloroethane andmixtures thereof. A solution of chloroform/acetonitrile 20/1 in volumewas found to be the best one for this purpose and polymers a₁ and a₄have the desired properties to efficiently dissolve a wide variety ofsilver salts, while PMMA shows the ability of dissolving copper salts. Amore complex problem is the solubility of nanoparticles both is organicsolvents and in solid matrices.

It has been found that despite the wide variety of ligands that can beattached on nanoparticles their solubility remains limited. In order toovercome this problem it is important to use nanoparticles with amixture of ligands. Examples of suitable ligands have been providedabove. The use of a mixture of ligands adds entropy to the system andmainly limits the interdigitation between ligands that is the main causefor poor solubility (Voicu, R., Badia, A., Morin, F., Lennox, R. B. &Ellis, T. H., Thermal behavior of a self-assembled silvern-dodecanethiolate layered material monitored by DSC, FTIR, and C-13 NMRspectroscopy. Chemistry of Materials, 12, 2646-2652 (2000); Sandhyarani,N., Pradeep, T., Chakrabarti, J., Yousuf, M. & Sahu, H. K., Distinctliquid phase in metal-cluster superlattice solids. Physical Review B,62, 8739-8742 (2000); Sandhyarani, N. & Pradeep, T., Crystalline solidsof alloy clusters. Chemistry of Materials, 12, 1755-1761 (2000); Badia,A. et al., Self-assembled monolayers on gold nanoparticles. Chemistry—aEuropean Journal, 2, 359-363 (1996)). In addition, particular groupswere used to make the particle more soluble in their host, e.g.carbazole terminated alkanethiol as one of the ligands to make theparticle soluble in polyvinylcarbazole.

The best strategy to synthesize these nanoparticles was the use of amonophase reaction in ethanol (Example 1), the simple addition ofdifferent ligands in different ratios was effective in obtainingparticles with different ligands on their outer shell and with adrastically reduced enthalpy of melting (Example 2).

If the particles are soluble enough, the casting of the films becomesrelatively easy and can be done either via solvent evaporation (Example8) or by spin coating (Example 17). In the first case the achievablerange of thickness spans from few microns (Example 13) to 200 μm. Themaximum silver salt loading ratio achievable in polymer a₁ is 15% (byweight) for silver tetrafluoroborate; in the same polymer 5% is themaximum for dye 1d, and 3% is the maximum for nAg6 (Example 9). Theloading ratio maxima are slightly higher in the case of spin coatingtechniques.

The solid state growth of metal nanoparticle has been explored andproven through a series of experiments involving the photochemicalreduction of silver ions in a matrix. The carbazole moiety plays therole of sacrificial anode too, thus allowing the possibility of dopingthe silver with a smaller amount of photoreducing dye.

Polyvinylcarbazole has a T_(g) of around 200° C. so a plasticizer wasused in order to lower the glass transition temperature to close to roomtemperature. A well known plasticizer for this polymer has been used:ethylcarbazole. The range of compositions of the film that was mostlyused was (all percentages in weight) 30-50% of plasticizer, 3-5% dye 1d,10-15% AgBF₄, 0.2-3% nAg6. The amount of plasticizer includes all valuesand subvalues therebetween, especially including 33, 36, 39, 42, 45 and48% by weight. The amount of dye includes all values and subvaluestherebetween, especially including 3.2; 3.4; 3.6; 3.8; 4.0; 4.2; 4.4;4.6 and 4.8% by weight. The amount of AgBF₄ includes all values andsubvalues therebetween, especially including 10.5; 11; 11.5; 12, 12.5;13; 13.5; 14 and 14.5% by weight. The amount of nAg6 includes all valuesand subvalues therebetween, especially including 0.4; 0.6; 0.8; 1.0;1.2; 1.4; 1.6; 1.8; 2.0; 2.2; 2.4; 2.6 and 2.8% by weight.

Reference films with the same composition but without nanoparticle werealso made. All the films made in this way had good optical quality andwere perfectly homogeneous by naked eye inspection, though some defectcould be observed, none was perfect under the microscope (60×magnification).

All films were irradiated with a tightly focused infrared light source(from 700 to 800 nm 100 fs pulse-length) generated silver lines (Example22) and or islands (squares in particular) while the correspondingreference film did not generate any visible feature. Further inspectionsof the reference film either using optical spectroscopy or TEMmicroscopy lead to the conclusion that small nanoparticles which have alarge size dispersion are generated. The features generated in polymerfilms that contained metal nanoparticles could be separated from theirmatrix via dissolution of the matrix in an appropriate solvent mixtureand then studied with XPS (Example 10) and SEM techniques (Example 9).

XPS Results show that the generated features are made mainly of silverin its zerovalent (metallic). The latter technique shows thatthree-dimensional features can be formed and that the generated linesare continuous up to a micron level.

A more complex experiment was done in order to study our process with aTEM microscope: three identical films were castes of copper grids(Example 11) and two of them were exposed to irradiation with ananosecond laser (532 nm), the first one was irradiated by a singlelaser shot (125 mJ) and the second one by three shots.

The result was that the average radius of the particle doubled after onelaser shot but their number per unit area stayed the same, all inagreement with the proposed mechanism (FIG. 9).

Many variations are possible, including the use of near fieldexcitation. In order to check the feasibility of this variation thethreshold power required for the writing was check and it was discoveredto be approx. 10⁸ W/m² for single photon excitation (Example 20) and 10⁹W/m² for two photon excitation (Example 21). The power thresholds areconsistent with those available for near field writing.

The experimental section contains many different kinds of films thathave been prepared using different kind of polymers (Example 15) ormatrices, dyes (Example 14), salts or nanoparticles (Example 12).

Important issues in the developing step have been solved. In order toprovide a chemical bond between the structures and the substrate a twostep method for functionalizing the substrate was developed. In thefirst step a monolayer of thiol terminated molecules is created in theglass substrate. This monolayer is bound to the substrate via trimethoxysilane functionalities. In the second step a nanoparticle monolayer isintroduced on the first monolayer and the particles are chemically boundto the thiols. This kind of functionalized substrate drasticallyimproved the adhesion and success in the developing step. FIG. 8 is aschematic drawing of the attachment of a ligand capped metalnanoparticle to a thiol functionalized glass substrate.

In order to test for the importance of the presence of silvernanoparticles in the precursor, we irradiated film F13 (Example 25) formore than one hour in a UV chamber to see if any characteristicnanoparticle absorption band would arise in the optical absorptionspectrum or if any metal feature could appear. Only a bleaching of thedye band was observed and absolutely no evidence of continuos silvermetal or nanoparticle formation, (as evidenced by optical absorption)was observed, even under such extreme irradiation conditions.

Functionalized Metal Nanoparticles for the Fabrication of ContinuousMetal Features

Silver nanoparticles were synthesized with coatings of different organicligands. Some of the ligands possessed groups capable of reducing, fromtheir excited state, silver ions to the neutral atom. The structures ofthese ligands are shown in the schematic drawing below. Threedye-ligands are used to synthesize electron and photo-activenanoparticles. The names and the ligand shell composition of theparticles used in some experiments are listed in the legend below.

Metal ligands Given Name Silver I₁ + I₂ + I₉ nAg10 Silver  I₁ + I₂ + I₁₀nAg11 Silver  I₁ + I₂ + I₁₁ nAg12 Silver I₉ nAg13 R = NO₂      I₉N(CH₂CH₃)2 I₁₀ HC = O      I₁₁

The synthesis of the ligand coated particles was a place exchangereaction (Hostetler, M. J., Templeton, A. C. & Murray, R. W. Dynamics ofplace-exchange reactions on mono layer-protected gold cluster molecules.Langmuir 15, 3782-3789 (1999)). Starting from a solution of nAg7 and thedesired ligand we were able to synthesize particles with dye moleculesin their outside shell. A different synthesis was used to obtainnanoparticles completely coated by dye attached ligands (Example 29). Inthis case silver ions were reduced with NaBH₄ in the presence of ligandI₉.

Mixtures of these particles and a silver salt gave rise to largerparticles (up to the continuous limit) upon excitation (light orelectron beams) both in solution and the solid state. A few examples,that are not representative of the full potentiality of these particles,will be discussed hereafter. The main advantage of these materialssystems that is that films of these particles are precursors for bothe-beam and light-induced growth of continuous metal features.

In order to test the reactivity of composite materials containingdye-coated particles, a series of experiments were performed on a set offour films:

Films containing nanoparticles with reducing dyes on their ligand shell(nAg11) and 2% wt. of silver salt (AgBF₄). (F14, F18)

Films of nanoparticles with reducing dyes on their ligand shell (nAg11)and no silver salt. (F15, F19)

Films of nanoparticles with no reducing dyes on their ligand shell(nAg7) and 2% wt. of silver salt (AgBF₄). (F16, F20)

Films of nanoparticles with no reducing dyes on their ligand shell(nAg7) and no silver salt. (F17, F21)

The reactivity Of films with a thickness of ˜20 nm was tested in ascanning electron microscope (SEM). Film (i) was shown to be anefficient precursor for continuous metal features. In fact, combinationsof squares and lines could be written using the electron beam of themicroscope. The unreacted film could be washed away following patterningwith dichloromethane to reveal the remaining metal pattern. Thestructures before and after the washing are shown in FIG. 16. The leftimage of FIG. 16 shows an example of a square and a line written andimaged using an SEM on F14. The right image shows an example of a partof a square and a line imaged with an SEM after removal of the unexposedfilm. All the other films showed were inactive with respect to theelectron beam patterning.

The same films, cast on a glass substrate, were excited with laser beamsin order to test their photochemical activity for metal patterning. Onfilm (i) a series of lines was written using both visible (488 nm, 50mW, one photon excitation) and infrared (730 nm, 250 mW, two-photonexcitation) light. The written pattern was imaged before and afterremoval of the unreacted nanoparticles by washing. Again Film (i) wasshown to be photochemically active in forming metal patterns. Film (ii)was shown to be active as well as, but at higher incident laser power(80 and 400 mW for one- and two-photon excitation, respectively). Allthe lines were written at a speed of 2 μm/s. Films iii and iv were notphotochemically active in patterning metal.

Similar experiments were conducted on films using a the electron beam ofa transmission electron microscope (TEM), with films cast on supportingSi₃N₄ grids. The solution for film casting was the same as that used forthe SEM tests, but were diluted 10 fold in order prepare sub-monolayerfilms. In some areas of these films, dense regions of particles could befound and in others well separated nanoparticle were observed. In allfour films isolated nanoparticles with no neighboring particles showedno significant morphological change during electron beam exposure. Films(iii) and (iv) showed no morphological change even in the regions thatwere more dense in particles. Films (i) and (ii), in their more denseregions, showed growth of the silver particles and their coalescence toform semi-continuous regions. Film (i) was shown to react quickly underelectron irradiation. The reaction was slower in the film (ii).

The photochemical reactivity was tested on the same set of films castonto four separate grids. All the films were initially imaged quickly inthe TEM, in order to obtain initial reference images, and then they wereirradiated with 488 nm light for 240 min. with an intensity of 1.5W/cm². The films were then imaged again in the TEM. Only film (i) showedmorphological changes. FIG. 17 illustrates the average changes for film(i) after electron-beam and light-induced growth. FIG. 17 illustratesthe laser and electron-beam induced growth of silver nanoparticles in ananoparticle/salt composite. a, TEM image of a composite prior to laserexposure, showing a domain of ordered nanoparticles with a mean radiusof 6 nm. b, Image of composite following one-photon excitation at 488 mufor 240 min. with an intensity of 1.5 W/cm² (to ensure depletion of thesilver salt), showing growth of particles. c, Image of composite priorto electron-beam irradiation, showing a domain of ordered nanoparticleswith the same mean radius as in a. d, Image of composite followingelectron-beam irradiation in the TEM instrument for 15 min, showinggrowth of particles and formation of a nearly consolidated metal domain.Scale bars: 50 nm.

The same set of tests were repeated with films based on nAg10, nAg12 andnAg13 metal particles, and the results were identical to those describedabove.

A thick polyvinylcarbazole (PVK) film (F22) containing nAg12 and asilver salt was cast in order to test whether such a composite materialbased on the functionalized nanoparticles would function as a precursorfor the growth of continuous metal features. The film was mounted on amicrofabrication stage and irradiated with 730 nm light (80 mW). It wasfound that a line of silver could be written and this line was imagedwith optical microscopy (FIG. 18). FIG. 18 shows the transmissionoptical microscopy of a line written in a PVK film (F22) doped withAgBF₄ and nAg12. Scale bar 30 μm.

Growth of Reflective and Conductive Metal Islands and Wires in aPolymeric Matrix

Films with compositions described in Examples 39 and 40 were cast onglass slides for two-photon microfabrication. Squares patterns of silverwere written using rastered laser scanning. The reflectivity of thesesquares was probed with a He—Ne laser (632.8 nm). The incident power was2 mW and the incidence angle was ˜30°. The written squares of silvershowed a reflectance of 25% whereas the unexposed polymeric compositeshowed a reflectance of 3%. A reflection image of the square taken usinga confocal microscope (514.5 nm) and an interference filter for 514.5 nmwhich was placed between the scan head and the microscope and whichblocks any fluorescence and allows the passage of the reflected light tothe detector, is shown in FIG. 19 which illustrates the reflection imageof a silver square (right) embedded in a polymer nanocomposite.

The conductance of silver lines written on a glass substrate with anarray of conductive pads the surface was measured. A series of parallelsilver pads were deposited on a glass substrate using standardlithographic techniques. Half the slide was masked to allow subsequentcontacting to the pads. A series of 5 parallel lines, 200 μm long with asection of 1 μm², were fabricated at the substrate surface andperpendicular to the pads to make electrical contact between the writtenlines and the pads. The resistance of lines were measured between padsseparated by varying distances. Measurements were also made betweencontrol pads that were not connected by written lines. The bias voltagewas ramped from −2 V to +2 V, the measured current between the pads notconnected by microfabricated lines was in the range of the noise levelof the instrument (0.1 pA) indicating a huge resistance. The averageresistance measured between two neighboring pads connected by themicrofabricated lines (32 μm spacing) was 370Ω. The resistivity (ρ)microfabricated lines was determined to be about 10⁻³ Ωcm, withoutcorrection for contact resistance (FIG. 20). FIG. 20 is a schematicdrawing of the slide/polymer/microfabricated line configuration used tomeasure the conductivity of the grown wires.

Microfabrication of Copper and Gold Microstructures Via Two-PhotonExcitation.

Films loaded with copper nanoparticles, copper salts and a dye Id, asdescribed in Example 41, were cast and a pattern of copper wires wasmicrofabricated using two photon excitation. The same pattern wasmicrofabricated in a gold nanoparticle composite, described in example41. A 3D “stack of logs” structure was successfully microfabricated inboth composites and demonstrates that the methods described herein aregeneral and can be applied to a variety of metals. Both of thestructures are shown in FIG. 21 which is a plot of the measured I(V)curve, showing a resistance of 373Ω.

Holographic Data Storage Via Photoinduced Growth of SilverNanoparticles.

The use of metal nanoparticle containing composite materials forholographic data storage was demonstrated using films described inExample 43. Two laser beams crossing at 90° (see FIG. 22 for the opticalset up) were used for holographic exposure. One of the beams (the image)was expanded and passed through a resolution test mask and the otherbeam served a plane wave reference. The holographic exposure wasperformed with an Ar⁺ ion laser (514.5 nm) with a total power of 200 mW.After exposure, the image was reconstructed with a diffractionefficiency of 8% and the reconstructed image was captured using adigital camera (see FIG. 23).

FIG. 22 shows metallic structures fabricated in nanocomposites bytwo-photon scanning laser exposure a, TOM image of copper microstructurein a different polymer nanocomposite fabricated by two-photon laserexposure. b, TOM image of a gold microstructure fabricated by two-photonlaser exposure. Scale bars: 25 μm, scale bars.

FIG. 23 shows on the left an optical set up for the writing ofholograms. On the right an optical set up for the readings of hologramsis shown. The blue ellipsoids represent focusing lenses, while the grayrectangles are mirrors. The faint gray rectangle is a 50/50beam-splitter. The black rectangle on the right is a beam stop.

Syntheses

All reagents were purchased from Aldrich and used as received. Allsolvents used are reagent grade unless specified.

Silver Nanoparticles

Silver Nanoparticles Capped with a Single Type of Ligand (nAg1-4)

All the syntheses were done using the following procedure:

340 mg of AgNO₃ (2 mmol) were dissolved in 100 ml of absolute ethanol at0° C. under vigorous stirring. An amount that varied from 2/9 to ⅔ of amillimole of the chosen ligand was dissolved in a small amount ofethanol and added. A saturated ethanol (200 ml) solution of NaBH₄ wasprepared and, 30 min after the addition of the ligand, was added veryslowly (over 2 hours). The solution immediately turned yellow and thenslowly became very dark. The solution was left stirring for additional 2hours and then it was put in a refrigerator to flocculate.

On the next day the solution was vacuum filtered using a quantitativepaper filter (VWR) with pore diameter of 1 μm and the filtered powderwas washed twice with ethanol and various times with acetone.

The yields varied from 49 to 81%.

Example 1

Synthesis of Dodecanethiol-Coated Silver Nanoparticle (nAg₁)

330 mg of AgNO₃ (˜2 mmol) were dissolved in 200 ml of absolute ethanolat 0° C. under vigorous stirring. 58 mg of dodecanethiol ( 2/6 mmol)were dissolved in 10 ml of ethanol and added to the starting solution. Asaturated ethanol (200 ml) solution of NaBH₄ was prepared and, 30 minafter the addition of the ligand, was added very slowly (2 hours). Thesolution immediately turned yellow and then slowly became very dark. Thesolution was left stirring for other 2 hours and then it was put in arefrigerator to flocculate.

On the next day the solution was filtered under vacuum using aquantitative paper filter (VWR) with a pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various times withacetone.

190.65 mg of a black powder were collected, giving a yield of 71%.

Silver Nanoparticle Coated with Two or More Types of Ligands

The syntheses were done using one of two different strategies. The firststrategy a) involved a one step reaction in which nanoparticles aresynthesized in the presence of multiple ligands, the second strategy b)involved a two step reaction in which nanoparticle undergo a ligandexchange reaction to introduce a second type of ligand.

a) For the first strategy the following approach was used:

340 mg of AgNO₃ (2 mmol) were dissolved in 100 ml of absolute ethanol at0° C. under vigorous stirring. A 10 ml solution of the desired mixtureof ligands was prepared. The molar ratio of the ligands

$\left( \frac{\eta_{ligandA}}{\eta_{ligandB}} \right)$was between 1 and 0.25 and the total amount was chosen so that the ratiobetween the moles of ligands and the moles of silver was between 2/9 to⅔. 30 min after the addition of the ligand, a saturated ethanol (200 ml)solution of NaBH₄ was prepared and, was added very slowly (over 2hours). The solution immediately turned yellow and then slowly becamevery dark. The solution was left stirring for other 2 hours and then itwas put in a refrigerator to flocculate.

On the next day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various time withacetone.

Some types of nanoparticles did not flocculate upon cooling and in thosecases the solvent was evaporated under vacuum and then the residue wassuspended in water under sonication for 15 min. The water was then leftin the hood for 2 h to flocculate and then filtered according to thestandard procedure.

The yields varied from 30 to 75%.

Example 2

Synthesis of Octanethiol-Thiol Coated Silver Nanoparticle (nAg₆)

340 mg of AgNO₃ (2 mmol) were dissolved in 200 ml of absolute ethanol at0° C. under vigorous stirring. 24 mg of octanethiol (⅙ mmol) weredissolved in 10 ml of ethanol together with 156 mg of I₄ (½ mmol) andadded to the starting solution. A saturated ethanol (200 ml) solution ofNaBH₄ was prepared and, 30 min after the addition of the ligands, wasadded very slowly (2 hours). The solution immediately turned yellow andthen slowly became very dark. The solution was left stirring for other 2hours and then it was put in a refrigerator to flocculate.

On the next day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various time withacetone.

Yield: 273 mg of a black-greenish powder.

b) The Second Strategy was an Exchange Reaction

This kind of reaction was done following a known method (Hostetler, M.J., Templeton, A. C. & Murray, R. W. Dynamics of place-exchangereactions on mono layer-protected gold cluster molecules. Langmuir 15,3782-3789 (1999)).

Example 3

Synthesis of Octanethiol-Thiol Coated Silver Nanoparticle (nAg9)

Ligand exchange reaction on silver nanoparticles nAg1: The silvernanoparticles nAg1 (85.4 mg) coated with octanethiol were dissolved bystirring overnight in CH₂Cl₂. Then the ligand I₈ (14.2 mg, 0.024 mmol)is added and the dark brown solution is stirred for 5 days in theabsence of light. The CH₂Cl₂ was removed in vacuum and the brown residueis dispensed in EtOH. The particles set down overnight and can befiltered off with quantitative filterpaper and washed several times withacetone.

Yield: 17 mg. Elemental analysis: nAg9: C, 26.30; H, 4.31; S, 7.38; Ag,53.99 nAg1: C, 22.85; H, 4.62; S, 7.23; Ag, 62.50 Octanethiol: C, 66.19;H, 11.79; S, 22.07 I_(g): C, 70.66; H, 6.48; S, 9.81.

Calculation based on the elemental analysis give a weight ratio for theligands of ca. 85 Octanethiol and 15% TMF-I-48. The calculated molarratios are:n ₁₈ /n _(Octanethiol)=0.043n _(Ag) /n _(Octanethiol) +n ₁₈=1.78 in nAg9n _(Ag) /n _(Octanethiol)=2.25 in nAg1

¹NMR (CDCl₃): The ¹H NMR reveals the spectrum of the ligand I_(g).

Preparation of Gold Nanoparticles

Gold nanoparticles were prepared according to the procedure of Brust(Brust, M., Walker, M., Bethel, D., Schiffrin, D. J. & Whyman, R.Synthesis of Thiol-Derivatized Gold Nanoparticles in a 2-PhaseLiquid-Liquid System. Journal of the Chemical Society—ChemicalCommunications, 801-802 (1994)).

Example 4

Synthesis Dodecanethiol-Coated Gold Nanoparticle (nAul)

352.8 mg of HAuCl₄*3H₂O (0.9 mmol) were dissolved in 30 ml of deionizedwater, 2.188 g of tetraoctylammoniumbromide (4 mmol) were dissolved in80 ml of toluene. The two phases were mixed and stirred for 1 h. 170 mgof dodecanethiol (0.84 mmol) were dissolved in 10 ml of toluene andadded. After 10 min 380 mg of NaBH₄ were dissolved in 25 ml of water andadded all at once. Soon the organic layer became black. After 2 h theorganic layer was separated and washed 3 times. The toluene was reducedto 10 ml under vacuum and immediately diluted to 500 ml with ethanol andthe solution put in a refrigerator overnight. On the next day thesolution was filtered on a qualitative filter paper and washed withtoluene multiple times.

10 mg of a black powder were collected.

Copper Nanoparticles

Copper Nanoparticle Capped with a Single Type of Ligand

237 mg of CuBF₄*H₂O (1 mmol) were dissolved in 100 ml of absoluteethanol (degassed by argon bubbling for at least an hour) at 0° C. undervigorous stirring in Argon atmosphere. An amount that varied from 2/9 to⅔ of a millimole of the chosen ligand was dissolved in a small amount ofethanol and added. Solution immediately turned bright yellow. After 2 ha saturated (100 ml) NaBH₄ solution of degassed ethanol was prepared andwas added very slowly (over 3 hours). The solution immediately turneddark yellow and then slowly became very dark. The solution was leftstirring for other 2 hours and then it was put in a refrigerator toflocculate.

On the following day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various times withacetone. The whole reaction was made in controlled atmosphere.

Example 5

Synthesis of Dodecanethiol-Coated Copper Nanoparticle (nCu1)

228 mg of CuBF₄*H₂O (0.96 mmol) were dissolved in 100 ml of absoluteethanol (degassed by argon bubbling for at least 2 h) at 0° C. undervigorous stirring in Argon atmosphere. 51 mg of octanethiol (˜⅓ mmol)were dissolved in a small amount of ethanol and added. Solutionimmediately turned bright yellow. After 2 h a saturated (100 ml) NaBH₄solution of degassed ethanol was prepared and was added very slowly (3hours). The solution immediately turned yellow and then slowly becamevery dark. The solution was left stirring for other 2 hours and then itwas put in a refrigerator to flocculate.

On the following day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various times withacetone. The whole reaction was made in controlled atmosphere.

The yield was 40 mg of a black powder.

Copper Nanoparticle Coated with Two or More Types of Ligands.

237 mg of CuBF₄*H₂O (1 mmol) were dissolved in 100 ml of absoluteethanol (degassed by argon bubbling for at least an hour) at 0° C. undervigorous stirring in Argon atmosphere. A 10 ml solution of the desiredmixture of ligands was prepared and added.

The molar ratio of the ligands

$\left( \frac{\eta_{ligandA}}{\eta_{ligandB}} \right)$was between 1 and 0.25 and the total amount was chosen so that the ratiobetween the moles of ligand and the moles of silver was between 2/9 to⅔. After 2 h a saturated (100 ml) NaBH₄ solution of degassed ethanol wasprepared and was added very slowly (over 3 hours). The solutionimmediately turned yellow and then slowly became very dark. The solutionwas left to for other 2 hours and then it was put in a refrigerator toflocculate.

On the following day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various time withacetone. The whole reaction was made in controlled atmosphere.

Example 6

Synthesis of Octanethiol-Carbazolethiol Coated Copper Nanoparticle(nCu3)

240 mg of CuBF₄*H₂O (0.974 mmol) were dissolved in 100 ml of absoluteethanol (degassed by argon bubbling for at least 2 h) at 0° C. undervigorous stirring in Argon atmosphere. 76 mg of octanethiol (˜½ mmol)and 35 mg of dodecanethiol (˜⅙ mmol) were dissolved in a small amount ofethanol and added. Solution immediately turned bright yellow. After 2 ha saturated (100 ml) NaBH₄ solution of degassed ethanol was prepared andwas added very slowly (3 hours). The solution immediately turned yellowand then slowly became very dark. The solution was left to for other 2hours and then it was put in a refrigerator to flocculate.

On the following day the solution was filtered under vacuum using aquantitative paper filter (VWR) with pore diameter of 1 μm and thefilter powder was washed twice with ethanol and various time withacetone. The whole reaction was made in controlled atmosphere.

The yield was 45 mg of a black powder.

Dye and Ligand Syntheses

Most of the molecules and polymers used in the Examples were preparedaccording to literature methods, the synthesis of the new molecules isdescribed here:

I₉

C₂₇H₂₄O₄

Exact Mass: 412.17

Mol. Wt.: 412.48

C, 78.62; H, 5.86; O, 15.52

4-{2-[4-[2-(4-formylphenyl)vinyl]-2-(3-hydroxypropoxy)phenyl]vinyl}benzaldehyde

(TMF-I-39): A solution of mono(diethyl)acetal terephthalaldehyde (1.75ml, 8.8 mmol) and diethyl2-(3-{[tert-butyl(dimethyl)silyl]oxy}-propoxy)-4-[(diethoxyphosphoryl)methyl]benzylphosphonate (2.49 g, 4.4 mmol) in tetrahydrofuran (THF) (100 ml) wascooled to 0° C. with an ice bath. K₂CO₃ (10 ml 1 M solution in THF, 10mmol)) was added slowly via a syringe and reaction is allowed to warm upto room temperature. After stirring overnight water was added followedby 1 M HCl (50 ml) and the reaction mixture was stirred for anotherhour. The product was extracted with CH₂Cl₂ and chromatographed onsilica. The first fraction eluted with CH₂Cl₂ was rejected and theproduct was then collected using ethylacetate as solvent.Crystallization from CH₂Cl₂ gave the pure product as yellow solid (663g).

¹H NMR (CDCl₃): 10.01 (1H, s), 10.00 (1H, s), 7.88 (4H, t, J=7.5 Hz),7.67 (4H, t, J=7.5 Hz), 7.60-7.64 (3H, m), 7.12-7.24 (4H, m), 4.30 (2H,t, J=6.0 Hz), 3.97 (2H, t, J=6.0 Hz), 2.20 (2H, tt, J=6.0, 6.0 Hz), 1.61(1H, br s) ppm; element. anal.: calcd. C, 78.62; H, 5.86, found C,78.36; H, 5.67.

C₃₅H₃₆O₅S₂

Exact Mass: 600.20

Mol. Wt.: 600.79

C, 69.97; H, 6.04; O, 13.32; S, 10.67

3-{2,5-bis[(E)-2(4-formylphenyl)ethenyl]phenoxy}-propyl5-(1,2-dithiolan-3-yl) pentanoate

A solution of4-{2-[4-[2-(4-formylphenyl)vinyl]-2-(3-hydroxypropoxy)phenyl]vinyl}-benzaldehyde(above) (200 mg, 0.49 mmol), lipoic acid (100 mg, 0.49 mmol) andp-toluenesulfonic acid (20 mg, 0.10 mmol) was refluxed overnight in theminimum amount of CH₂Cl₂ (≈20 ml) necessary to dissolve the chromophore.The reaction mixture was poured onto a column (Al₂O₃/CH₂Cl₂) and flashchromatographed with CH₂Cl₂:Ethylacetate/10:1. The starting material wasrecovered using ethyl alcohol (EtOH). Yield: 90 mg (31%) yellow solid.

¹H NMR (CDCl₃): 9.974 (1H, s, CHO), 9.969 (1H, s, CHO), 7.86 (2H, d,J=8.5 Hz), 7.85 (2H, d, J=8.5 Hz), 7.65 (4H, d, J=8.0 Hz), 7.57-7.62(2H, m), 7.04-7.24 (5H, m), 4.36 (2H, t, J=6.5 Hz), 4.19 (2H, t, J=6.0Hz), 3.49 (1H, m), 3.12 (1H, m), 3.05 (1H, m), 2.39 (1H, m), 2.31 (2H,t, J=7.0 Hz), 2.25 (2H, m), 1.84 (1H, m), 1.57-1.69 (4H, m), 1.35-1.48(2H, m) ppm. ¹³C NMR (CDC₃l): 191.86 (CHO), 191.77 (CHO), 173.65,156.78, 144.08, 143.28, 138.09, 135.60, 135.38, 131.86, 130.47, 128.27,128.00, 127.36, 127.16, 126.52, 126.30, 120.16, 110.30, 65.19, 61.33,56.52, 40.42, 38.66, 34.76, 34.21, 29.89, 28.94, 24.85 ppm.

Polymer Synthesis (a2)

Synthesis of Carbazole Monomer c_(m):

To a solution of carbazole acid (5.0 g, 14.23 mmol) and 2hydroxyethylmethacrylate (2.0 g, 15.37 mmol) and4-dimethylamino-pyridine (0.2 g) in THF (30 ml) was added DCC (3.7 g,17.96 mmol) at room temperature. The reaction was carried out at thistemperature for 10 h. Solid was removed by filtration. After removal ofTHF, the crude product was purified by silica gel column usinghexane/ethyl acetate (9:1) as eluent. The pure product as colorless oilwas obtained in 4.2 g (63.6%).

¹H-NMR (CDCl₃, TMS, 500 MHZ): δ=8.12 (d, 2 H_(arom), J=7.5 Hz), 7.47 9m,2 H_(arom)), 7.42 (d, 2 H_(arom), J=7.5 Hz), 7.24 (m, 2 H_(arom)), 6.13(s, 1 H, C═C—H), 5.60 (s, 1 H, C═C—H), 4.35 (m, 4 H, 2×OCH₂), 4.30 (t, 2H, NCH₂, J=7.5 Hz), 2.33 (t, 2 H, COCH₂, J=7.0 Hz), 1.95 (s, 3H, CH₃),1.88 (m, 2 H, CH₂), 1.61 (m, 2 H, CH₂), 1.24 (m, 12 H, 6×CH₂) ppm.

¹³C-NMR (CDCl₃, 126 MHZ): δ=173.58, 167.07, 140.34, 135.87, 126.02,125.51, 122.73, 120.29, 118.63, 108.59, 62.42, 61.82, 43.01, 34.09,29.38, 29.35, 29.30, 29.14, 29.00, 28.92, 27.26, 24.84, 18.25 ppm.

Elemental Analysis for C₂₉H₃₇NO₄ (463.61): Cald: C, 75.13; H, 8.04; N,3.02. Found: C, 75.08; H, 7.83; N, 3.28.

Synthesis of Carbazole Polymer PCUEMA:

Carbazole monomer (2.7 g, 5.82 mmol) and AIBN (14.3 mg, 0.087 mmol) weredissolved in dry benzene (5.0 ml) under nitrogen. The reaction mixturewas cooled with liquid nitrogen. After one freeze-thaw-pump cycle thereaction was heated at 60° C. for 60 h. The polymer was precipitated inmethanol and collected by filtration. The polymer was dissolved in THFsolution and precipitated in methanol. Thedissolution/precipitation/filtration sequence was repeated twice. Afterdrying, the white polymer was obtained in 2.65 g (98.1%) yield.

¹H-NMR (CDCL₃, TMS. 500 MHZ): δ=7.97 (d, 2 H_(arom), J=8.0 Hz), 7.31 (m,2 H_(arom)), 7.24 (d, 2 H_(arom), J=8.0 Hz), 7.09 (m, 2 H_(arom)), 4.07(m, 4 H, 2×OCH₂), 4.01 (s, br, 2 H, NCH₂), 2.17 (s, br, 2 H, COCH₂),1.68 (m, 2H, CH₂), 1.45 (s, br, 2 H, CH₂), 1.07 (m, 12 H, 6×CH₂), 0.93(s, br, 2 H, CH₂), 0.80 (s, br, 3 H, CH₃) ppm. ¹³C-NMR (CDCl₃, 126 MHZ):δ=173.25, 140.30, 128.30, 125.48, 122.70, 120.26, 118.63, 108.56, 62.65,61.16, 44.82, 42.89, 33.78, 29.44, 29.35, 29.28, 29.08, 28.90, 27.22,24.74 ppm.

I₄ and I₅

Example 7

Synthesis of Ligand I₄

3.57 g 9-carbazole-yl-octane-1-thiol (˜10 mmol) were dissolved in 20 mlof dimethylsulfoxide (DMSO), 1.52 mg of thiourea (˜20 mmol) were added,the solution was vigorously stirred. After 2 days a concentrated aqueoussolution of NaOH was added dropwise. Soon a red precipitated formed,during the addition the precipitated redissolved again and solutionturned red. Addition was stopped upon reaching of pH 11 (checked usingpH paper). The solution was then neutralized adding dropwise HCl (aq.cone) and it slowly turned yellow. The organic was then extracted withdiethyl ether (Et₂O) and washed with water three times. The organicsolvent was dried under vacuum, and the residue was collected.

Sample Preparation

In this section several examples of nanocomposite sample processing andpreparation are given. All films hereafter reported have been tested andmetallic silver lines have been successfully written using radiation inall cases on.

Samples were prepared by solvent casting or by spin coating, Most of thesamples were cast in air atmosphere, in some cases the processing wasdone under argon atmosphere.

All glass microscope slides were cleaned with the following procedure:

a) Sonication for 1 h in water and soap and extensive rinse with DIwater

b) Sonication for 1 h in spectroscopic grade methanol and rinse withabsolute ethanol or isopropanol.

Glass slides with monolayer coatings of nanoparticles were processedafter cleaning as follows (hereafter referred as monolayered slides):

a) Dipped for 10 min in a saturated isopropanol (reagent) solution ofKOH, and then rinsed with DI water and dried using a nitrogen flow.

b) A solution of 75 ml of toluene, 0.5 ml of isopropylamide and 2 ml of2-mercaptopropyltrimethylsiloxane was prepared and kept at 60° C. for anhour.

c) the slides were dipped in the solution for 1 h at 60° C., and thenrinsed with hexane (spectrophotometric grade).

d) The samples were immersed overnight in hexane.

e) A CH₂Cl₂ solution (2 mg/ml of nanoparticle nAg6) was solvent castedby solvent evaporation on the slides

f) The samples were immersed overnight in hexane.

ITO (Indium Tin Oxide) slides were cleaned simply by rinsing them inethanol on them.

Nanocomposite Film Casting by Solvent Evaporation

A fixture for hold samples for casting by solvent evaporation wasfabricated and used for all such castings this plate held substratesfixed in a horizontal position and allowed for control of theatmosphere. Under each slide 3 ml of reagent grade chloroform wereplaced prior to casting so to initially maintain the saturation of theatmosphere with solvent vapor upon introduction of the casting syrup.Each slide compartment was closed using a watch glass, so that thevolume of air in which each slide was casted was approx. 15 cm³.

Solvents were degassed by freeze-pump-thaw cycle.

Example 8

FI Standard 100 μm Film

188.86 mg of polymer a₁ (poly 9-vinylcarbazole), 89.6 mg ofethylcarbazole, 2.59 mg of nAg6, and 8.77 mg of dye 1d were dissolved in6 ml of degassed chloroform under argon atmosphere and left stirringovernight.

On the following day 22 mg of AgBF₄ were dissolved in 0.02 ml ofdegassed acetonitrile and mixed to the chloroform solution. After 30 minthe solution was filtered with a membrane filter (1 μm pore size). 0.6ml of the filtered solution were casted on a 25×25 mm ITO slide.

Example 9

F2 Standard 100 μm Film

660 mg of polymer a₁ (poly 9-vinylcarbazole), 329 mg of ethylcarbazole,2.8 mg of nAg6, and 28 mg of dye 1d were dissolved in 6 ml of degassedchloroform under argon atmosphere and left stirring overnight.

On the following day 110 mg of AgBF₄ were dissolved in 0.33 ml ofdegassed acetonitrile and 0.3 ml of those were added to the chloroformsolution. After 10 min the solution was filtered with a membrane filter(1 μm pore size). 2 ml of the filtered solution were casted on a 75×25mm glass slide.

Example 10

F3 20 μm Film with High Loading of Nanoparticles

92 mg of polymer a₁ (poly 9-vinylcarbazole) were dissolved in 5 ml ofdichloromethane (DCM), 12 mg of AgBF₄ were dissolved in 5 ml of DCM and1 ml of acetonitrile, 5 mg of dye 1d were dissolved in 5 ml of DCM, 5.5mg of nAg1 were dissolved in 2 ml of chloroform. All solution werestirred for 2 h and then mixed together. 2 ml of the solution werecarted on a 75×25 mm glass slide.

Example 11

F4 Films for TEM

11.5 mg of polymer a₁ (poly 9-vinylcarbazole), 2.4 mg of AgBF₄, 2.8 mgof dye Id, 1 mg of nAg1 were dissolved in 10 ml of DCM; solution wasdiluted 10 times and 2 μl of this solution were carted on a carboncoated copper grid. Three identical films were made in this way.

FIG. 9 shows TEM images illustrating growth of metal nanoparticle in acomposite film upon exposure to either one or three laser pulses from ans pulsed laser. The upper TEM image shows the system after one lasershot, the lower after three. In the upper limit the average radius hasbecome 4.9 nm, in the non-irradiate sample it was 2.9. In the lowerimage the average diameter is even bigger and larger metal islands canbe seen.

Example 12

FS Standard 100 μm Film with a Different Kind of Nanoparticle

648 mg of polymer a₁ (poly 9-vinylcarbazole), 316 mg of ethylcarbazole,2.75 mg of nAg7, and 20.7 mg of dye id were dissolved in 6 ml ofdegassed chloroform under argon atmosphere and left stirring overnight.

On the following day 219 mg of AgBF₄ were dissolved in 0.6 ml ofdegassed acetonitrile and 0.2 ml were mixed to the chloroform solution.After 30 min the solution was filtered with a membrane filter (1 μm poresize). 0.4 ml of the filtered solution were carted on a 25×25 mm ITOslide.

Example 13

F6 Standard 10 μm Film

64.5 mg of polymer a₁ (poly 9-vinylcarbazole), 38.1 mg ofethylcarbazole, 1.21 mg of nAg6, and 3.31 mg of dye Id were dissolved in6 ml of degassed chloroform under argon atmosphere and left stirringovernight.

On the following day 20.4 mg of AgBF₄ were dissolved in 0.3 ml ofdegassed acetonitrile and 0.1 ml were mixed to the chloroform solution.After 30 min the solution was filtered with a membrane filter (1 μmpores). 0.4 ml of the filtered solution were casted on a 75×25 mm glassslide.

Example 14

F7 Standard 100 μm Film with a Different Dye

411.16 mg of polymer a, (poly 9-vinylcarbazole), 206.48 mg ofethylcarbazole, 2.28 mg of nAg6, and 19.72 mg of dye 2b were dissolvedin 6 ml of degassed chloroform under argon atmosphere and left stirringovernight.

On the following day 50.8 mg of AgBF₄ were dissolved in 0.3 ml ofdegassed acetonitrile and mixed to the chloroform solution. After 30 minthe solution was filtered with a membrane filter (1 μm pores). 0.6 ml ofthe filtered solution were casted on a 75×25 mm monolayered glass slide.

Example 15

F8 Standard 100 μm Film with a Different Polymer

95.1 mg of polymer a₂ (PCUEMA), 0.71 mg of nAg6, and 1.8 mg of dye 1dwere dissolved in 1 ml of degassed chloroform under argon atmosphere andleft stirring overnight.

On the following day 9.5 mg of AgBF₄ were dissolved in 0.05 ml ofdegassed acetonitrile and mixed to the chloroform solution. After 30 minthe solution was filtered with a membrane filter (1 μm pores). 0.6 ml ofthe filtered solution were casted on a 25×25 mm monolayered glass slide.

Example 16

F9 Standard 100 μm Film for Copper Generation

66.6 mg of polymer a₄ (poly methylmethacrylate), 1.1 mg of nCu1, and3.08 mg of dye 1d were dissolved in 0.6 ml of degassed chloroform underargon atmosphere and left stirring overnight.

On the following day 5 mg of ICuP(CH₃)₃ were dissolved in 0.05 ml ofdegassed acetonitrile and mixed to the chloroform solution. After 30 minthe solution casted on a 25×25 mm glass slide

Spin Coated Films

Example 17

F10 Standard Spin Coated Film

100 mg of polymer a₁ (poly 9-vinylcarbazole), 6 mg of ethylcarbazole, 3mg of nAg4, and 4.5 mg of dye 1d were dissolved in 1 ml of chloroformand left stirring overnight.

On the following day 100 mg of AgBF₄ were dissolved in 1 ml ofacetonitrile and 0.1 ml were added to the chloroform solution. After 30min the solution was spin coated on a 25×25 mm glass slide at 2000 RPMfor 20 s. The obtained thickness was ˜8 μm, as proved by prism couplermeasurements.

Nanoparticle Containing Viscous Liquid

Example 18

F11 Standard Viscous Liquid Matrix Film

A quantity of host c₁ was heated using an heatgun and as soon as itflowed freely it was pipetted in a vial into order to weigh a fixedamount.

226 mg of host c₁, 2 mg of nAg6, and 5.77 mg of dye 1d were dissolved in2 ml of chloroform and left stirring overnight.

On the following day 11 mg of AgBF₄ were dissolved in 0.1 ml ofacetonitrile and mixed to the chloroform solution. After 30 min thesolution was casted on a 75×25 mm glass slide.

Class I Films

Example 19

F12 Standard Class I Film

5.23 mg of nAg1, and 0.5 mg of dye 1d, and 0.5 mg of AgBF₄ weredissolved in 2 ml of chloroform left stirring overnight.

On the following day the solution was casted on a 75×25 mm glass slide.

FIG. 10 shows a silver ribbon written with a two-photon irradiation (800mu, 120 fs) (Example 19).

Metal Writing in Nanoparticle Composites Using One and Two PhotonExcitation

All writing experiments were performed using a femtosecond mode-lockedTi:sapphire laser. Specifically a Spectra Physics system consisting of aTsunami (Ti:sapphire laser) pumped by a Millenia (diodes pumped YAGlaser) was used. The average pulse length was 120 fs with a bandwidth of˜20 nm. Unless specified otherwise the wavelength used was 760 nm.

The sample was mounted on a micropositioner (Sutter MP-285). The laserbeam was focused on the sample using an inverted microscope (Nikon). Acomputer controlled both the micropositioner and a shutter (Newport846HP). The combination of the micropositioner movements and theopening/closing cycles of the shutter allowed patterned exposures andmetallic structures to be written in the sample.

In order to locate the focus of the beam in the sample a two-photonmicroscopy setup was used, the beam was going through a Biorad MRC-1024scanhead.

Writing Using Single Photon Excitation

In the case of writing using single photon excitation, the laser outputlight was frequency doubled double using a LBO doubling crystal and theremaining fundamental light left was filtered away using a combinationof a crystal polarizer and an infrared short pass dielectric filter.

The rest of the set-up was identical to the two-photon writing process,above described. The focusing process was done using the scanhead in aconfocal fashion.

Example 20

Threshold Measurements for One-Photon Writing of Silver

Film F1 (Example 8) was mounted on the micropositioner, in the standardway. The laser output wavelength was set at 860 nm (420 mW) and was notchanged during the experiment. A filter wheel was placed in the set upso to be able to make continuous and controllable variations in theaverage power of the laser. The stage translation speed was set at 10μm/s. The beam was focused in the sample using a 60× objective (NA 1.4).It was possible to write lines in the film everywhere and the behaviorwas mostly uniform: so for a comparison with the two-photon experimentthe threshold was calculated at the glass/film interface. The power wasgradually decreased and the success of the writing process wasdetermined by optical microscopy. The writing threshold was found to be0.09 mW. If we make the hypothesis of a circular beamspot with adiameter of 1 μm, we find a threshold intensity of approx. 10⁸ W/m² forthese 120 fs pulses.

For a pattern of lines written spaced of 5 μm we were able to put anupper limit to their width using the optical images, this limit being500 nm.

FIG. 11 shows silver lines written using a one-photon excitation (430nm), lines are clearly visible. The dark spots are defects in the filmwhich was not of optimal quality.

Writing Using Two-Photon Excitation.

Dye utilized herein as two-photon excitable photoreducing agents wereknown to have a reasonably large two-photon cross-section thus allowingefficient two-photon excitation. This in combination with a high NAfocusing system, allows writing high resolution lines inthree-dimensional patterns in the matrix.

Example 21

Threshold Measurements for Two-Photon Writing of Silver

Film F1 (Example 8) was mounted on the micropositioner, in the standardway. The laser output wavelength was set at 760 nm (620 mW) and was notchanged during the experiment. A filter wheel was placed in the set upso to be able to make continuous and controllable variations in theaverage power of the laser. The stage translation speed was set at 10μm/s. The beam was focused in the sample using a 60× objective (NA 1.4).Lines were written everywhere in the film the behavior was mostlyuniform, so to have the possibility to further develop the structuresthe threshold was calculated at the glass/film interface. The power wasgradually decreased and the success of the writing process wasdetermined by optical microscopy. The writing threshold was found to be1.55 mW. If we make the hypothesis of a circular beamspot with adiameter of 1 μm, we find an intensity threshold of approx. 1.5 10⁹W/m².

For a pattern of lines written spaced of 5 μm we were able to put anupper limit to their width using the optical images, this limit being 1μm.

Example 22

Multiphoton Writing and Developing

Film F3 (Example 10) was mounted on the micropositioner, in the standardway. The laser output wavelength was set at 800 nm (400 mW) and was notchanged during the experiment. The writing speed was set at 100 μm/s.The microscope objective used was a 10×. Lines were written at theglass/film interface. A regular pattern of 6 sets of 5 lines each waswritten. Each set was places 30 μm away from the previous and the lineswere spaced 10 mm away to each other, all the lines were 500 μm long.After writing the film was placed in a DCM containing beaker and leftthere for 3 days. In doing these the polymer was washed away and thelines stayed on the substrate.

Example 23

Multi Photon Writing and Developing

Film F2 (Example 9) was mounted on the micropositioner, in the standardway. The laser output wavelength was set at 760 nm (620 mW) and was notchanged during the experiment. The stage translation speed was set at 10μm/s. The beam was focused in the sample using a 60× objective (NA 1.4)and an immersion oil was used. Lines were written everywhere in the filmthe behavior was mostly uniform. Many different patterns were written,the most significant one being a cage “like” structure with a 13 layerof sets of lines each layer being 5 μm higher than the previous, eachlayer consisting of 20 lines 100 μm long and spaced of 5 μm, each layerconsisting of lines perpendicular to the ones of the previous layer.

After the writing process was done the film was removed from themicropositioner, cleaned from the immersion oil using a paper tissue andthen put in a solution of DCM and acetonitrile (10:1). The polymerdissolved away leaving the structure on the substrate.

FIG. 4 illustrates an optical transmission image, (top view) of a 3Dstructure (200×200×65 μm) written in a polymer a₁ matrix. The writingprocess was done using a two-photon excitation (760 nm, 120 fs).

FIG. 5 illustrates an optical image of the same structure shown in FIG.4 on a larger scale, the optical quality of the matrix is clearly quitegood.

FIG. 6 is a SEM image of a 3D metallic silver microstructure formed bytwo-photon writing in a composite film, they revealed by washing toproduce a free standing structure on the surface.

Example 24

Multiphoton Writing of Copper Structures

Film F9 (Example 16) was mounted on the micropositioner, in the standardway. The laser output wavelength was set at 760 nm (620 mW) and was notchanged during the experiment. A square of copper was written using thea 10× lens. The result was checked via optical imaging.

FIG. 12 shows an optical micrograph of a copper square (200×200 μm)written by two-photon excitation.

Example 25

Control Experiment, F13

10 mg of PVK where dissolved in 10 ml of dichloromethane, 1 mg of AgBF₄was dissolved in the same solution, 1 mg of dye 1 was then added. Thesolution was casted on a 75×25 mm glass slide.

The film was put in a UV chamber and irradiated at 419 nm with 15 lamps(5 W each). The optical absorption was followed and the results aresummarized in FIG. 13, just the bleaching of the nanoparticle band wasobserved.

FIG. 13 shows a spectrum of the sample from control experiment showingthe absence of formation of metal nanoparticle in a film containing dyesand metal salt but no initial concentration of metal nanoparticle. Notethe absence of the absorption band of metal nanoparticles followingexposure. The solid line represent the spectrum of the film 13, thebands around 300 nm are due to the polymer itself while the band at 426is characteristic of dye 1. The dashed line represents the same filmirradiated for 30 min while the dotted one for 60 min.

Characterization

XPS

Metallic Silver lines written according to the procedures describedabove (Example 22) were analyzed using XPS spectroscopy and their AugerParameter was measured to be 726.2 meV, perfectly matching the tabulatedone for Ag⁰. Images of the written lines could be recorded using thespectrometer in an imaging mode.

FIG. 7 shows a XPS spectrum (above) and image (below) a set of silverlines. The Auger parameter obtained from the spectrum is 726.2, which isthe same as that tabulated one for zerovalent silver.

SEM

The structures were coated with a very thin metallic layer (Au/Ir alloy)for SEM imaging. FIG. 14 shows an SEM picture of the corner of a 3Dmetallic silver structure written using two-photon excitation. Themultiple layers written are evident.

TEM Characterization of Metal Nanoparticle Growth.

A nanosecond YAG laser (20 Hz) doubled light (532 nm) was used in singleshot fashion for the following experiment. One of the amorphous carboncoated copper grid with the composite film on it (estimated thickness 50nm) was not used and left as a reference, the second one received asingle laser pulse, the third one received three laser pulses. Theaverage energy of each pulse was 120 μJ. The average radius of theparticle in the reference grid was found to be 2.95 nm; in the secondgrid it was 4.95 nm, in the third grid it was found to be approx. 9.5nm. Moreover the number of nanoparticle per unit area was found not toincrease.

FIG. 15 shows a TEM image of chemically synthesized nanoparticles (nAg1)used as a precursor in the composites. A solution of nanoparticlessample was sonicated for a minute in acetone and then one drop of thesolution was dried on a copper grid coated with amorphous carbon. Themicroscope used was an Hitachi 8100.

Conductivity of Silver Lines

Tests were performed that demonstrated that the silver lines wereelectrically conductive. In one test, probes from a volt-ohm meter werecontacted to a written pad of silver and impedance of ˜80 MΩ wasmeasured over a distance of 200 mm. Since good electrical contact wasnot assured, this gives an upper limit on the impedance of this lengthof the line.

Exchange Reaction nAg7 with Thiol Functionalized Dyes, GeneralProcedure:

The silver nanoparticles were dissolved in CH₂Cl₂ and stirred for twohour to ensure complete dissolution. The dye was added and the flaskcovered with aluminum foil. After stirring for 4 days the solvent wasremoved in vacuum with the moderate heating to a maximum of 35° C.Acetone was added and the precipitated nanoparticles collected onquantitative filter paper and washed with acetone until the solventshowed no sign of fluorescence in ultraviolet light. The nanoparticleswere dried in air and analyzed by elemental analysis.

Example 26

1₁₁ Functionalized Nanoparticles (nAg12)

Octylthiol/dodecylthiol protected silver nanoparticles (nAg7) (250 mg),4-((E)-2-{4-[(E)-2-(4-formylphenyl)ethenyl]-2-[(11-mercaptoundecyl)oxy]-5-methoxyphenyl}ethenyl)benzaldehyde(1₁₁) (14.1 mg, 0.025 mmol), CH₂Cl₂ (500 ml). Anal. (%) for nAg12(duplicated analysis): C, 11.78 (11.70), H, 2.07 (2.01), S: 2.76 (2.86),Ag: 76.62 (76.13).

Example 27

1₁₀ Functionalized Nanoparticles (nAg11)

Octylthiol/dodecylthiol protected silver nanoparticles (nAg7) (150 mg),11-(2,5-bis{(E)-2-[4-(diethylamino)phenyl]ethenyl}-4-methoxyphenoxy)undecan-1-thiol(1₁₀) (50 mg, 0.076 mmol), CH₂Cl₂ (300 ml). Isolated yield: 80.5 mg.Anal. (%) for nAg11 (duplicated analysis): C, 19.41 (19.45), H, 2.85(2.76), N, 0.62 (0.62), S: 3.06 (3.24), Ag: 71.10 (71.06).

Example 28

1₉ Functionalized Nanoparticles (nAg10)

Octylthiol/dodecylthiol protected silver nanoparticles (nAg7) (150 mg),11-{4-methoxy-2,5-bis[(E)-2-(4-nitrophenyl)ethenyl]phenoxy}-1-undecanethiol(1₉) (46 mg, 0.076 mmol), CH₂Cl₂ (300 ml). Anal. (%) for nAg10(duplicated analysis): C, 20.38 (20.40), H, 2.41 (2.26), N, 0.99 (0.96),S: 2.98 (2.86), Ag: 63.92 (63.97).

Example 29

1₉-Only Functionalized Nanoparticles (nAg13)

116.5 mg of silver nitrate were dissolved in ˜75 ml ethanol at 0° C. 138mg of 1₉ were dissolved in a mixture of ˜100 ml acetone and 5 ml ofdichloromethane. The dye solution was added to the silver nitratesolution and allowed to stir for 45 minutes. 75 ml of a saturated sodiumborohydride solution in ethanol were added dropwise over a four hoursperiod. The solution was allowed to stir for an additional three hours.The solution was stored in a refrigerator overnight and allowed todecant. The precipitate was filtered and washed with water, acetone, anddichloromethane. 146.3 mg of a black powder were collected. Anal. (%)for nAg13: C: 41.00, H: 4.10%, N: 2.88%, S: 3.57%, Ag: 37.51%.

Composition and Preparation of Films of Nanoparticles

Example 30

F14 Film of Dye Attached Nanoparticles Class (i), 20 nm Thick

1 mg of nAg12 was dissolved in 20 cc of chloroform and left to stir for2 days. 2 mg of AgBF₄ were dissolved in 10 cc of acetonitrile; 0.1 cc ofthis solution were added to the nanoparticle solution. 0.5 cc of thecombined solution was cast on a 25×25 mm ITO coated glass slides.

Example 31

F15 Film of Dye Attached Nanoparticles Class (ii), 20 nm Thick

1 mg of nAg12 was dissolved in 20 cc of chloroform and left to stir for2 days. The film was prepared casting 0.5 cc of the solution on a 25×25mm ITO coated glass slides.

Example 32

F16 Film of Dye Attached Nanoparticles Class (iii), 20 nm Thick

1 mg of nAg7 was dissolved in 20 cc of chloroform and left to stir for 2days. 2 mg of AgBF₄ were dissolved in 10 cc of acetonitrile; 0.1 cc ofthis solution were added to the nanoparticle solution. 0.5 cc of thecombined solution was cast on a 25×25 mm ITO coated glass slides.

Example 33

F17 Film of Dye Attached Nanoparticles Class (iv), 20 nm Thick

1 mg of nAg7 was dissolved in 20 cc of chloroform and left to stir for 2days. The film was prepared casting 0.5 cc of the solution on a 25×25 mmITO coated glass slides.

Example 34

F18 Film of Dye Attached Nanoparticles Class (i), Submonolayer

1 mg of nAg12 was dissolved in 20 cc of chloroform and left to stir for2 days. 2 mg of AgBF₄ were dissolved in 10 cc of acetonitrile; 0.1 cc ofthis solution were added to the nanoparticle solution. 2 cc of thecombined solution were diluted 10 times with chloroform, and 2 μl weredeposited on a Si₃N₄ coated Si substrate (1 mm²).

Example 35

F19 Film of Dye Attached Nanoparticles Class (ii), Submonolayer

1 mg of nAg12 was dissolved in 20 cc of chloroform and left to stir for2 days. 2 cc of the solution were diluted 10 times with chloroform, and2 μl were deposited on a Si₃N₄ coated Si substrate (1 mm²).

Example 36

F20 Film of Dye Attached Nanoparticles Class (iii), Submonolayer

1 mg of nAg7 was dissolved in 20 cc of chloroform and left to stir for 2days. 2 mg of AgBF₄ were dissolved in 10 cc of acetonitrile; 0.1 cc ofthis solution were added to the nanoparticle solution. 2 cc of thecombined solution were diluted 10 times with chloroform, and 2 μl weredeposited on a Si₃N₄ coated Si substrate (1 mm²).

Example 37

F21 Film of Dye Attached Nanoparticles Class (iv), Submonolayer

1 mg of nAg7 was dissolved in 20 cc of chloroform and left to stir for 2days. 2 cc of the solution were diluted 10 times with chloroform, and 2μl were deposited on a Si₃N₄ coated Si substrate (1 mm²).

Example 38

F22 Polymer Based Film for Nanoparticle Growth

1 mg of nAg12 was dissolved in 20 cc of chloroform and left to stir for2 days. 200.6 mg of PVK and 89 mg of ethylcarbazole were dissolved in 2cc of the nanoparticle solution and left to stir for 1 day. 210 mg ofAgBF₄ were dissolved in 1 cc of acetonitrile; 0.1 cc of this solutionwere added to the nanoparticle/polymer solution. The whole solution wascast on a 25×75 mm glass slide.

Example 39

F23 Film for Reflectivity

271 mg of PCUEMA, 20.5 mg of ethylcarbazole, 1.67 mg of nAg6, and 7.16mg of 1d were dissolved in 6 cc of chloroform and left to stirovernight. 27 mg of AgBF₄ were dissolved in 0.2 cc of acetonitrile andadded to the solution. The combined solution was filtered using a 1 μmpores filter and 2 cc of the filtered solution were cast on a 25×75 mmglass slide.

Example 40

F24 Film for Conductivity

2 mg of nAg6 were dissolved in 5 cc of chloroform and left to stir for 1day. The solution was filtered with a 1 mm pores filter. 21 mg of PVK, 9mg of ethylcarbazole, and 1.3 mg of 1d were dissolved in 0.3 cc of thenanoparticles solution and left to stir for 2 hours. 20 mg of AgBF₄ weredissolved in 0.5 cc of acetonitrile, 0.05 cc of this solution were addedto the polymer nanoparticle solution. The solution was cast of half of atailor made glass slide (25×25 mm), while the other half was coveredwith Teflon tape.

The slide had on it a pattern of 40 parallel silver lines 150 μm wide,15 mm long and 50 nm height. The lines were spaced of 32 μm, and werefabricated using standard e beam lithography techniques

Example 41

F25 Copper Microfabrication Film

The film was formed by dissolving 66 mg of poly(methylmethacrylate)PMMA, 1.1 mg of ligand coated copper nanoparticles nCu1, 5 mg ofCuP(CH₃)₃I, and 3 mg of dye id in 0.6 ml of degassed CHCl₃ and cast on a25×25 mm glass slide under an argon atmosphere.

Example 42

F26 Gold Microfabrication Film

The film was formed by dissolving 66 mg of PMMA, 1.1 mg of ligand coatedgold nanoparticles nAul, 5 mg of AuP(CH₃)₃Br, and 3 mg of dye 1d in 0.6ml of CHCl₃ and cast on a 25×25 mm glass slide under an argonatmosphere.

Example 43

F27 Film for Holography

271 mg of PVK, 20.5 mg of ethylcarbazole, 1.67 mg of nAg6, and 0.8 mg of1d were dissolved in 6 cc of chloroform and left to stir overnight. 27mg of AgBF₄ were dissolved in 0.2 cc of acetonitrile and added to thesolution. The combined solution was filtered using a 1 pores filter and2 cc of the filtered solution were cast on a 25×75 mm glass slide.

Provisional U.S. patent application 60/256,148, filed Dec. 15, 2000, andthe patents and literature references cited in the Detailed Description,are incorporated herein by reference.

Obviously, numerous modifications and variations on the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The invention claimed is:
 1. A method for growth of a pre-nucleatedmetal nanoparticle, comprising: providing a composite including thepre-nucleated metal nanoparticle, wherein said pre-nucleated metalnanoparticle includes organic ligand bonded nanoparticles and thecomposite includes a metal salt and a photon absorbing dye, generating ametal atom by reducing a metal ion in the composite by exposure toradiation; and reacting said metal atom with said pre-nucleated metalnanoparticle in the composite, thereby growing a metal nanoparticle inthe composite, said organic ligand bonded nanoparticles comprising amixture of two or more types of ligand coated metal nanoparticles,wherein at least one organic ligand of the organic ligand bondednanoparticles is represented by the formula A-B-C, wherein A is amolecular or ionic fragment, B is an organic fragment that has twopoints of attachments for connecting to point A and for connecting topoint C, and C is a molecular fragment with one point of attachment thatconnects to fragment B.
 2. The method according to claim 1, furthercomprising collapsing of at least two metal nanoparticles, therebyobtaining metallic continuous phase.
 3. The method according to claim 1,wherein said metal atom is generated from the metal ion by using anelectron-beam.
 4. The method according to claim 1, wherein said metalatom is generated by laser excitation of a molecule, thereby generatingheat and causing thermal reduction of the metal ion.
 5. The methodaccording to claim 1, wherein said metal atom is generated byphoto-excitation of a molecule, thereby creating an excited state ofsaid molecules and increasing a reducing potential of said molecule; andreducing of said metal ion by said molecule in said excited state toobtain the metal atom.
 6. The method according to claim 1, wherein saidphoton absorbing dye comprises an electron deficient two-photonabsorbing dye in the composite.
 7. The method according to claim 6,wherein said organic ligand bonded nanoparticles comprise organic ligandbonded Ag nanoparticles, said metal salt comprises a AgBF4 salt, andsaid photon absorbing dye comprises an electron deficient two-photonabsorbing dye in polyvinylcarbazole.
 8. The method according to claim 1,wherein said generating a metal atom and said reacting the metal atomcomprises irradiating the composite with laser pulses at a wavelength of730 nm.
 9. The method according to claim 1, wherein said generating ametal atom and said reacting the metal atom comprises irradiating thecomposite with laser pulses at wavelength ranges from 157 nm to 1.5 μmfor one-photon excitation.
 10. The method according to claim 1, whereinsaid generating a metal atom and said reacting the metal atom comprisesirradiating the composite with laser pulses at wavelength ranges from300 nm to 3.0 μm for two-photon excitation.
 11. The method according toclaim 1, wherein said growing a metal nanoparticle in the compositecomprises moving a point of focus of the radiation.
 12. The methodaccording to claim 11, wherein said moving comprises moving the point offocus to at least one of write microscale lines, write rectangularshapes, and write three dimensional patterns of metal lines.
 13. Amethod for growth of a pre-nucleated metal nanoparticle, comprising:forming a film from said pre-nucleated metal nanoparticle, a metal salt,a photon absorbing dye and a polymer matrix, said pre-nucleated metalnanoparticle including organic ligand bonded nanoparticles; generating ametal atom by reducing metal ion in the composite by exposure toradiation; and reacting said metal atom with said pre-nucleated metalnanoparticle, thereby growing a metal nanoparticle, said organic ligandbonded nanoparticles comprising a mixture of two or more types of ligandcoated metal nanoparticles, wherein at least one organic ligand of theorganic ligand bonded nanoparticles is represented by the formula A-B-C,wherein A is a molecular or ionic fragment, B is an organic fragmentthat has two points of attachments for connecting to point A and forconnecting to point C, and C is a molecular fragment with one point ofattachment that connects to fragment B.